Implement complete collection persistence with database-backed survival across server restarts

• Add full multi-table schema for collections with normalized design (collections, collection_templates, collection_items, collection_item_versions)
• Implement collection detection and processing in enhancement pipeline for .insertr-add elements
• Add template extraction and storage from existing HTML children with multi-variant support
• Enable collection reconstruction from database on server restart with proper DOM rebuilding
• Extend ContentClient interface with collection operations and full database integration
• Update enhance command to use engine.DatabaseClient for collection persistence support

internal/db/sqlite/setup.sql.go

@@ -9,6 +9,83 @@ import (
 	"context"
 )
 
+const initializeCollectionItemVersionsTable = `-- name: InitializeCollectionItemVersionsTable :exec
+CREATE TABLE IF NOT EXISTS collection_item_versions (
+    version_id INTEGER PRIMARY KEY AUTOINCREMENT,
+    item_id TEXT NOT NULL,
+    collection_id TEXT NOT NULL,
+    site_id TEXT NOT NULL,
+    html_content TEXT NOT NULL,
+    template_id INTEGER NOT NULL,
+    position INTEGER NOT NULL,
+    created_at INTEGER DEFAULT (strftime('%s', 'now')) NOT NULL,
+    created_by TEXT DEFAULT 'system' NOT NULL,
+    FOREIGN KEY (item_id, collection_id, site_id) REFERENCES collection_items(item_id, collection_id, site_id) ON DELETE CASCADE
+)
+`
+
+func (q *Queries) InitializeCollectionItemVersionsTable(ctx context.Context) error {
+	_, err := q.db.ExecContext(ctx, initializeCollectionItemVersionsTable)
+	return err
+}
+
+const initializeCollectionItemsTable = `-- name: InitializeCollectionItemsTable :exec
+CREATE TABLE IF NOT EXISTS collection_items (
+    item_id TEXT NOT NULL,
+    collection_id TEXT NOT NULL,
+    site_id TEXT NOT NULL,
+    template_id INTEGER NOT NULL,
+    html_content TEXT NOT NULL,
+    position INTEGER NOT NULL,
+    created_at INTEGER DEFAULT (strftime('%s', 'now')) NOT NULL,
+    updated_at INTEGER DEFAULT (strftime('%s', 'now')) NOT NULL,
+    last_edited_by TEXT DEFAULT 'system' NOT NULL,
+    PRIMARY KEY (item_id, collection_id, site_id),
+    FOREIGN KEY (collection_id, site_id) REFERENCES collections(id, site_id) ON DELETE CASCADE,
+    FOREIGN KEY (template_id) REFERENCES collection_templates(template_id) ON DELETE RESTRICT
+)
+`
+
+func (q *Queries) InitializeCollectionItemsTable(ctx context.Context) error {
+	_, err := q.db.ExecContext(ctx, initializeCollectionItemsTable)
+	return err
+}
+
+const initializeCollectionTemplatesTable = `-- name: InitializeCollectionTemplatesTable :exec
+CREATE TABLE IF NOT EXISTS collection_templates (
+    template_id INTEGER PRIMARY KEY AUTOINCREMENT,
+    collection_id TEXT NOT NULL,
+    site_id TEXT NOT NULL,
+    name TEXT NOT NULL,
+    html_template TEXT NOT NULL,
+    is_default INTEGER DEFAULT 0 NOT NULL,
+    created_at INTEGER DEFAULT (strftime('%s', 'now')) NOT NULL,
+    FOREIGN KEY (collection_id, site_id) REFERENCES collections(id, site_id) ON DELETE CASCADE
+)
+`
+
+func (q *Queries) InitializeCollectionTemplatesTable(ctx context.Context) error {
+	_, err := q.db.ExecContext(ctx, initializeCollectionTemplatesTable)
+	return err
+}
+
+const initializeCollectionsTable = `-- name: InitializeCollectionsTable :exec
+CREATE TABLE IF NOT EXISTS collections (
+    id TEXT NOT NULL,
+    site_id TEXT NOT NULL,
+    container_html TEXT NOT NULL,
+    created_at INTEGER DEFAULT (strftime('%s', 'now')) NOT NULL,
+    updated_at INTEGER DEFAULT (strftime('%s', 'now')) NOT NULL,
+    last_edited_by TEXT DEFAULT 'system' NOT NULL,
+    PRIMARY KEY (id, site_id)
+)
+`
+
+func (q *Queries) InitializeCollectionsTable(ctx context.Context) error {
+	_, err := q.db.ExecContext(ctx, initializeCollectionsTable)
+	return err
+}
+
 const initializeSchema = `-- name: InitializeSchema :exec
 CREATE TABLE IF NOT EXISTS content (
     id TEXT NOT NULL,