refactor: reorganize Rust codebase into modular handlers and database layers

- Split monolithic src/db.rs (1122 lines) into domain modules: projects, tags, settings
- Extract API handlers from main.rs into separate handler modules by domain
- Add proxy module for ISR/SSR coordination with Bun process
- Introduce AppState for shared application context
- Add utility functions for asset serving and request classification
- Remove obsolete middleware/auth.rs in favor of session checks in handlers

web/src/lib/api.server.ts

@@ -19,7 +19,7 @@ export async function apiFetch<T>(
 
   const url = `${baseUrl}${path}`;
   const method = init?.method ?? "GET";
-  
+
   // Unix sockets require Bun's native fetch (SvelteKit's fetch doesn't support it)
   const fetchFn = isUnixSocket ? fetch : (init?.fetch ?? fetch);