feat(ui): add web UI with Jinja2 templates and Gitea themes

- Add Jinja2 templates with data-testid attributes for testing
- Create light/dark themes based on Gitea color scheme
- Add theme switching with localStorage persistence
- Create base CSS, components, and layout styles
- Add mock web routes for UI demonstration
- Register web router and static files in main.py
- Add data-testid requirements to AGENTS.md
- Install jinja2 dependency

app/main.py

@@ -12,6 +12,8 @@ from dishka import make_async_container
 from dishka.integrations.fastapi import setup_dishka
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import HTMLResponse
+from fastapi.staticfiles import StaticFiles
 
 from app.infrastructure import close_db, init_db, register_exception_handlers, settings
 from app.infrastructure.di.providers import (
@@ -22,6 +24,7 @@ from app.infrastructure.di.providers import (
     UseCaseProvider,
 )
 from app.presentation import router
+from app.presentation.web import router as web_router
 
 
 @asynccontextmanager
@@ -77,6 +80,19 @@ def app_factory() -> FastAPI:
     )
 
     app.include_router(router, prefix="/api")
+    app.include_router(web_router)
+    app.mount("/static", StaticFiles(directory="static"), name="static")
+
+    @app.get("/", response_class=HTMLResponse)
+    async def root_redirect() -> HTMLResponse:
+        """Redirect root URL to web UI.
+
+        Returns:
+            HTMLResponse with redirect to web interface.
+        """
+        return HTMLResponse(
+            content='<meta http-equiv="refresh" content="0;url=/web/">', status_code=200
+        )
 
     @app.get("/health", tags=["health"])
     async def health_check() -> dict[str, str]: