Consolidate type definitions and fix API contract

- Move all ContentItem, ContentClient, ContentResponse types to engine/types.go as single source of truth
- Remove duplicate type definitions from content/types.go
- Update all imports across codebase to use engine types
- Enhance engine to extract existing data-content-id from HTML markup
- Simplify frontend to always send html_markup, let server handle ID extraction/generation
- Fix contentId reference errors in frontend error handling
- Add getAttribute helper method to engine for ID extraction
- Add GetAllContent method to engine.DatabaseClient
- Update enhancer to use engine.ContentClient interface
- All builds and API endpoints verified working

This resolves the 400 Bad Request errors and creates a unified architecture where the server is the single source of truth for all ID generation and content type management.

internal/content/client.go

@@ -8,6 +8,8 @@ import (
 	"net/url"
 	"strings"
 	"time"
+
+	"github.com/insertr/insertr/internal/engine"
 )
 
 // HTTPClient implements ContentClient for HTTP API access
@@ -29,7 +31,7 @@ func NewHTTPClient(baseURL, apiKey string) *HTTPClient {
 }
 
 // GetContent fetches a single content item by ID
-func (c *HTTPClient) GetContent(siteID, contentID string) (*ContentItem, error) {
+func (c *HTTPClient) GetContent(siteID, contentID string) (*engine.ContentItem, error) {
 	url := fmt.Sprintf("%s/api/content/%s?site_id=%s", c.BaseURL, contentID, siteID)
 
 	req, err := http.NewRequest("GET", url, nil)
@@ -60,7 +62,7 @@ func (c *HTTPClient) GetContent(siteID, contentID string) (*ContentItem, error)
 		return nil, fmt.Errorf("reading response: %w", err)
 	}
 
-	var item ContentItem
+	var item engine.ContentItem
 	if err := json.Unmarshal(body, &item); err != nil {
 		return nil, fmt.Errorf("parsing response: %w", err)
 	}
@@ -69,9 +71,9 @@ func (c *HTTPClient) GetContent(siteID, contentID string) (*ContentItem, error)
 }
 
 // GetBulkContent fetches multiple content items by IDs
-func (c *HTTPClient) GetBulkContent(siteID string, contentIDs []string) (map[string]ContentItem, error) {
+func (c *HTTPClient) GetBulkContent(siteID string, contentIDs []string) (map[string]engine.ContentItem, error) {
 	if len(contentIDs) == 0 {
-		return make(map[string]ContentItem), nil
+		return make(map[string]engine.ContentItem), nil
 	}
 
 	// Build query parameters
@@ -107,13 +109,13 @@ func (c *HTTPClient) GetBulkContent(siteID string, contentIDs []string) (map[str
 		return nil, fmt.Errorf("reading response: %w", err)
 	}
 
-	var response ContentResponse
+	var response engine.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]ContentItem)
+	result := make(map[string]engine.ContentItem)
 	for _, item := range response.Content {
 		result[item.ID] = item
 	}
@@ -122,7 +124,7 @@ 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]ContentItem, error) {
+func (c *HTTPClient) GetAllContent(siteID string) (map[string]engine.ContentItem, error) {
 	url := fmt.Sprintf("%s/api/content?site_id=%s", c.BaseURL, siteID)
 
 	req, err := http.NewRequest("GET", url, nil)
@@ -149,13 +151,13 @@ func (c *HTTPClient) GetAllContent(siteID string) (map[string]ContentItem, error
 		return nil, fmt.Errorf("reading response: %w", err)
 	}
 
-	var response ContentResponse
+	var response engine.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]ContentItem)
+	result := make(map[string]engine.ContentItem)
 	for _, item := range response.Content {
 		result[item.ID] = item
 	}