Refactor architecture: eliminate auto-discovery and consolidate packages

- Remove auto-discovery entirely (~450 lines)
  * Delete internal/content/discoverer.go
  * Simplify enhancer to single-phase processing
  * Remove duplicate container expansion logic

- Consolidate repository implementations
  * Move internal/content/client.go → internal/db/http_client.go
  * Group all repository implementations in db/ package

- Add file utilities to engine following Go stdlib patterns
  * Add engine.ProcessFile() and ProcessDirectory() methods
  * Engine now handles both content processing AND file operations

- Move site management to dedicated package
  * Move internal/content/site_manager.go → internal/sites/manager.go
  * Clear separation of site lifecycle from content processing

- Preserve container expansion (syntactic sugar)
  * .insertr on containers still auto-applies to viable children
  * Container detection logic consolidated in engine/utils.go

Result: Clean architecture with single source of truth for .insertr processing

cmd/enhance.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/spf13/cobra"
 
+	"github.com/insertr/insertr/internal/config"
 	"github.com/insertr/insertr/internal/content"
 	"github.com/insertr/insertr/internal/db"
 )
@@ -95,7 +96,7 @@ func runEnhance(cmd *cobra.Command, args []string) {
 	var client db.ContentRepository
 	if cfg.API.URL != "" {
 		fmt.Printf("🌐 Using content API: %s\n", cfg.API.URL)
-		client = content.NewHTTPClient(cfg.API.URL, cfg.API.Key)
+		client = db.NewHTTPClient(cfg.API.URL, cfg.API.Key)
 	} else if cfg.Database.Path != "" {
 		fmt.Printf("🗄️ Using database: %s\n", cfg.Database.Path)
 		database, err := db.NewDatabase(cfg.Database.Path)
@@ -110,7 +111,7 @@ func runEnhance(cmd *cobra.Command, args []string) {
 
 	// Load site-specific configuration
 	enhancementConfig := content.EnhancementConfig{
-		Discovery: content.DiscoveryConfig{
+		Discovery: config.DiscoveryConfig{
 			Enabled:    false, // Default: disabled for explicit class="insertr" markings only
 			Aggressive: false,
 			Containers: true,