Refactor database layer to eliminate type switching and simplify architecture

- Replace type switching with clean repository pattern using sqlc-generated code
- Move ContentRepository interface and domain models to db package
- Create separate SQLiteRepository and PostgreSQLRepository implementations
- Remove unnecessary RepositoryAdapter and ContentClient interface duplication
- Update all clients (HTTP, Mock) to implement db.ContentRepository directly
- Add context.Context parameters to all repository methods (Go best practice)
- Eliminate duplicate domain models and type conversions
- Remove type aliases - use db package types directly throughout codebase
- Update engine, content managers, and API handlers to use repositories directly

Benefits:
- Zero runtime type switching overhead
- Single source of truth for domain models
- Clean package boundaries and separation of concerns
- Standard Go interface patterns with context support
- Easier testing with mockable repository interface
- Maintainable: adding new database types requires no changes to existing code

internal/content/client.go

@@ -1,6 +1,7 @@
 package content
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -9,10 +10,10 @@ import (
 	"strings"
 	"time"
 
-	"github.com/insertr/insertr/internal/engine"
+	"github.com/insertr/insertr/internal/db"
 )
 
-// HTTPClient implements ContentClient for HTTP API access
+// HTTPClient implements db.ContentRepository for HTTP API access
 type HTTPClient struct {
 	BaseURL    string
 	APIKey     string
@@ -31,7 +32,7 @@ func NewHTTPClient(baseURL, apiKey string) *HTTPClient {
 }
 
 // GetContent fetches a single content item by ID
-func (c *HTTPClient) GetContent(siteID, contentID string) (*engine.ContentItem, error) {
+func (c *HTTPClient) GetContent(ctx context.Context, siteID, contentID string) (*db.ContentItem, error) {
 	url := fmt.Sprintf("%s/api/content/%s?site_id=%s", c.BaseURL, contentID, siteID)
 
 	req, err := http.NewRequest("GET", url, nil)
@@ -62,7 +63,7 @@ func (c *HTTPClient) GetContent(siteID, contentID string) (*engine.ContentItem,
 		return nil, fmt.Errorf("reading response: %w", err)
 	}
 
-	var item engine.ContentItem
+	var item db.ContentItem
 	if err := json.Unmarshal(body, &item); err != nil {
 		return nil, fmt.Errorf("parsing response: %w", err)
 	}
@@ -71,9 +72,9 @@ func (c *HTTPClient) GetContent(siteID, contentID string) (*engine.ContentItem,
 }
 
 // GetBulkContent fetches multiple content items by IDs
-func (c *HTTPClient) GetBulkContent(siteID string, contentIDs []string) (map[string]engine.ContentItem, error) {
+func (c *HTTPClient) GetBulkContent(ctx context.Context, siteID string, contentIDs []string) (map[string]db.ContentItem, error) {
 	if len(contentIDs) == 0 {
-		return make(map[string]engine.ContentItem), nil
+		return make(map[string]db.ContentItem), nil
 	}
 
 	// Build query parameters
@@ -109,13 +110,13 @@ func (c *HTTPClient) GetBulkContent(siteID string, contentIDs []string) (map[str
 		return nil, fmt.Errorf("reading response: %w", err)
 	}
 
-	var response engine.ContentResponse
+	var response db.ContentResponse
 	if err := json.Unmarshal(body, &response); err != nil {
 		return nil, fmt.Errorf("parsing response: %w", err)
 	}
 
 	// Convert slice to map for easy lookup
-	result := make(map[string]engine.ContentItem)
+	result := make(map[string]db.ContentItem)
 	for _, item := range response.Content {
 		result[item.ID] = item
 	}
@@ -124,7 +125,7 @@ func (c *HTTPClient) GetBulkContent(siteID string, contentIDs []string) (map[str
 }
 
 // GetAllContent fetches all content for a site
-func (c *HTTPClient) GetAllContent(siteID string) (map[string]engine.ContentItem, error) {
+func (c *HTTPClient) GetAllContent(ctx context.Context, siteID string) (map[string]db.ContentItem, error) {
 	url := fmt.Sprintf("%s/api/content?site_id=%s", c.BaseURL, siteID)
 
 	req, err := http.NewRequest("GET", url, nil)
@@ -151,13 +152,13 @@ func (c *HTTPClient) GetAllContent(siteID string) (map[string]engine.ContentItem
 		return nil, fmt.Errorf("reading response: %w", err)
 	}
 
-	var response engine.ContentResponse
+	var response db.ContentResponse
 	if err := json.Unmarshal(body, &response); err != nil {
 		return nil, fmt.Errorf("parsing response: %w", err)
 	}
 
 	// Convert slice to map for easy lookup
-	result := make(map[string]engine.ContentItem)
+	result := make(map[string]db.ContentItem)
 	for _, item := range response.Content {
 		result[item.ID] = item
 	}
@@ -166,37 +167,42 @@ func (c *HTTPClient) GetAllContent(siteID string) (map[string]engine.ContentItem
 }
 
 // CreateContent creates a new content item via HTTP API
-func (c *HTTPClient) CreateContent(siteID, contentID, htmlContent, originalTemplate, lastEditedBy string) (*engine.ContentItem, error) {
+func (c *HTTPClient) CreateContent(ctx context.Context, siteID, contentID, htmlContent, originalTemplate, lastEditedBy string) (*db.ContentItem, error) {
 	// For now, HTTPClient CreateContent is not implemented for enhancer use
 	// This would typically be used in API-driven enhancement scenarios
 	return nil, fmt.Errorf("CreateContent not implemented for HTTPClient - use DatabaseClient for enhancement")
 }
 
 // Collection method stubs - TODO: Implement these for HTTP API
-func (c *HTTPClient) GetCollection(siteID, collectionID string) (*engine.CollectionItem, error) {
+func (c *HTTPClient) GetCollection(ctx context.Context, siteID, collectionID string) (*db.CollectionItem, error) {
 	return nil, fmt.Errorf("collection operations not implemented in HTTPClient")
 }
 
-func (c *HTTPClient) CreateCollection(siteID, collectionID, containerHTML, lastEditedBy string) (*engine.CollectionItem, error) {
+func (c *HTTPClient) CreateCollection(ctx context.Context, siteID, collectionID, containerHTML, lastEditedBy string) (*db.CollectionItem, error) {
 	return nil, fmt.Errorf("collection operations not implemented in HTTPClient")
 }
 
-func (c *HTTPClient) GetCollectionItems(siteID, collectionID string) ([]engine.CollectionItemWithTemplate, error) {
+func (c *HTTPClient) GetCollectionItems(ctx context.Context, siteID, collectionID string) ([]db.CollectionItemWithTemplate, error) {
 	return nil, fmt.Errorf("collection operations not implemented in HTTPClient")
 }
 
-func (c *HTTPClient) CreateCollectionTemplate(siteID, collectionID, name, htmlTemplate string, isDefault bool) (*engine.CollectionTemplateItem, error) {
+func (c *HTTPClient) CreateCollectionTemplate(ctx context.Context, siteID, collectionID, name, htmlTemplate string, isDefault bool) (*db.CollectionTemplateItem, error) {
 	return nil, fmt.Errorf("collection operations not implemented in HTTPClient")
 }
 
-func (c *HTTPClient) GetCollectionTemplates(siteID, collectionID string) ([]engine.CollectionTemplateItem, error) {
+func (c *HTTPClient) GetCollectionTemplates(ctx context.Context, siteID, collectionID string) ([]db.CollectionTemplateItem, error) {
 	return nil, fmt.Errorf("collection operations not implemented in HTTPClient")
 }
 
-func (c *HTTPClient) CreateCollectionItem(siteID, collectionID, itemID string, templateID int, htmlContent string, position int, lastEditedBy string) (*engine.CollectionItemWithTemplate, error) {
+func (c *HTTPClient) CreateCollectionItem(ctx context.Context, siteID, collectionID, itemID string, templateID int, htmlContent string, position int, lastEditedBy string) (*db.CollectionItemWithTemplate, error) {
 	return nil, fmt.Errorf("collection operations not implemented in HTTPClient")
 }
 
-func (c *HTTPClient) CreateCollectionItemAtomic(siteID, collectionID string, templateID int, lastEditedBy string) (*engine.CollectionItemWithTemplate, error) {
+func (c *HTTPClient) CreateCollectionItemAtomic(ctx context.Context, siteID, collectionID string, templateID int, lastEditedBy string) (*db.CollectionItemWithTemplate, error) {
 	return nil, fmt.Errorf("collection operations not implemented in HTTPClient")
 }
+
+// WithTransaction executes a function within a transaction (not supported for HTTP client)
+func (c *HTTPClient) WithTransaction(ctx context.Context, fn func(db.ContentRepository) error) error {
+	return fmt.Errorf("transactions not supported for HTTP client")
+}