docs(dev): integrate rest of the documentation

docs/Developer Guide/Developer Guide/Architecture/Backend.md

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+# Backend
+### Application Entry Point
+
+Location: `apps/server/src/main.ts`
+
+**Startup Sequence:**
+
+1.  Load configuration
+2.  Initialize database
+3.  Run migrations
+4.  Load Becca cache
+5.  Start Express server
+6.  Initialize WebSocket
+7.  Start scheduled tasks
+
+### Service Layer
+
+Located at: `apps/server/src/services/`
+
+**Core Services:**
+
+*   **Notes Management**
+    *   `notes.ts` - CRUD operations
+    *   `note_contents.ts` - Content handling
+    *   `note_types.ts` - Type-specific logic
+    *   `cloning.ts` - Note cloning/multi-parent
+*   **Tree Operations**
+    *   `tree.ts` - Tree structure management
+    *   `branches.ts` - Branch operations
+    *   `consistency_checks.ts` - Tree integrity
+*   **Search**
+    *   `search/search.ts` - Main search engine
+    *   `search/expressions/` - Search expression parsing
+    *   `search/services/` - Search utilities
+*   **Sync**
+    *   `sync.ts` - Synchronization protocol
+    *   `sync_update.ts` - Update handling
+    *   `sync_mutex.ts` - Concurrency control
+*   **Scripting**
+    *   `backend_script_api.ts` - Backend script API
+    *   `script_context.ts` - Script execution context
+*   **Import/Export**
+    *   `import/` - Various import formats
+    *   `export/` - Export to different formats
+    *   `zip.ts` - Archive handling
+*   **Security**
+    *   `encryption.ts` - Note encryption
+    *   `protected_session.ts` - Session management
+    *   `password.ts` - Password handling
+
+### Route Structure
+
+Located at: `apps/server/src/routes/`
+
+```
+routes/
+├── index.ts              # Route registration
+├── api/                  # REST API endpoints
+│   ├── notes.ts
+│   ├── branches.ts
+│   ├── attributes.ts
+│   ├── search.ts
+│   ├── login.ts
+│   └── ...
+└── custom/               # Special endpoints
+    ├── setup.ts
+    ├── share.ts
+    └── ...
+```
+
+**API Endpoint Pattern:**
+
+```typescript
+router.get('/api/notes/:noteId', (req, res) => {
+    const noteId = req.params.noteId
+    const note = becca.getNote(noteId)
+    res.json(note.getPojoWithContent())
+})
+```
+
+### Middleware
+
+Key middleware components:
+
+*   `auth.ts` - Authentication
+*   `csrf.ts` - CSRF protection
+*   `request_context.ts` - Request-scoped data
+*   `error_handling.ts` - Error responses