refactor: implement database-specific schema architecture with schema-as-query pattern

🏗️ **Major Database Schema Refactoring**

**Problem Solved**: Eliminated model duplication and multiple sources of truth by:
- Removed duplicate models (`internal/models/content.go`)
- Replaced inlined schema strings with sqlc-generated setup functions
- Implemented database-specific schemas with proper NOT NULL constraints

**Key Improvements**:
✅ **Single Source of Truth**: Database schemas define all types, no manual sync needed
✅ **Clean Generated Types**: sqlc generates `string` and `int64` instead of `sql.NullString/sql.NullTime`
✅ **Schema-as-Query Pattern**: Setup functions generated by sqlc for type safety
✅ **Database-Specific Optimization**: SQLite INTEGER timestamps, PostgreSQL BIGINT timestamps
✅ **Cross-Database Compatibility**: Single codebase supports both SQLite and PostgreSQL

**Architecture Changes**:
- `db/sqlite/` - SQLite-specific schema and setup queries
- `db/postgresql/` - PostgreSQL-specific schema and setup queries
- `db/queries/` - Cross-database CRUD queries using `sqlc.arg()` syntax
- `internal/db/database.go` - Database abstraction with runtime selection
- `internal/api/models.go` - Clean API models for requests/responses

**Version Control System**: Complete element-level history with user attribution and rollback

**Verification**: ✅ Full API workflow tested (create → update → rollback → versions)
**Production Ready**: Supports SQLite (development) → PostgreSQL (production) migration

README.md

@@ -52,9 +52,11 @@ Containers with `class="insertr"` automatically make their viable children edita
 
 **✅ Complete Full-Stack CMS**
 - **Professional Editor**: Modal forms, markdown support, authentication system
-- **Content Persistence**: SQLite database with REST API
+- **Content Persistence**: SQLite database with REST API, version control
+- **Version History**: Complete edit history with user attribution and one-click rollback
 - **CLI Enhancement**: Parse HTML, inject database content, build-time optimization
 - **Smart Detection**: Auto-detects content types (text/markdown/link)
+- **Deterministic IDs**: Content-based ID generation for consistent developer experience
 - **Full Integration**: Seamless development workflow with hot reload
 
 **🔄 Ready for Production**
@@ -114,10 +116,35 @@ Running `just dev` gives you the **complete Insertr CMS**:
 
 - ✅ **Professional Editor** - Modal forms, markdown support, authentication
 - ✅ **Real-Time Persistence** - SQLite database with REST API
+- ✅ **Version Control** - Complete edit history with user attribution and rollback
 - ✅ **Content Management** - Create, read, update content via browser
 - ✅ **Build Integration** - CLI enhances HTML with database content
 - ✅ **Hot Reload** - Changes reflected immediately
 
+## 📚 **Version Control Features**
+
+### **Complete Edit History**
+Every content change is automatically tracked with:
+- **User Attribution** - Who made each change
+- **Timestamps** - When changes were made
+- **Content Snapshots** - Full content preserved for each version
+
+### **Easy Rollback**
+- **View History** button in any content editor
+- **One-Click Restore** to any previous version
+- **Version Comparison** - See what changed between versions
+- **Safe Rollback** - Current content is preserved before restoration
+
+### **Example Workflow**
+```
+1. Editor clicks on any element with class="insertr"
+2. Professional editing modal opens
+3. Click "View History" to see all previous versions
+4. Each version shows: timestamp, author, content preview
+5. Click "Restore" on any version to rollback instantly
+6. All changes are tracked automatically
+```
+
 ### **Parse Existing Site**
 ```bash
 # Analyze HTML for editable elements