Rewrite from Go + vanilla JS to Python (FastAPI) + React (TypeScript)

- Backend: Python 3.12 with FastAPI, SQLAlchemy, boto3
- Frontend: React 18 with TypeScript, Vite build tooling
- Updated Dockerfile for multi-stage Node + Python build
- Updated CI pipeline for Python backend
- Removed old Go code (cmd/, internal/, go.mod, go.sum)
- Updated README with new tech stack documentation

backend/app/main.py

@@ -0,0 +1,54 @@
+from fastapi import FastAPI
+from fastapi.staticfiles import StaticFiles
+from fastapi.responses import FileResponse
+from contextlib import asynccontextmanager
+import os
+
+from .config import get_settings
+from .database import init_db
+from .routes import router
+
+settings = get_settings()
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    # Startup: initialize database
+    init_db()
+    yield
+    # Shutdown: cleanup if needed
+
+
+app = FastAPI(
+    title="Orchard",
+    description="Content-Addressable Storage System",
+    version="1.0.0",
+    lifespan=lifespan,
+)
+
+# Include API routes
+app.include_router(router)
+
+# Serve static files (React build) if the directory exists
+static_dir = os.path.join(os.path.dirname(__file__), "..", "..", "frontend", "dist")
+if os.path.exists(static_dir):
+    app.mount("/assets", StaticFiles(directory=os.path.join(static_dir, "assets")), name="assets")
+
+    @app.get("/")
+    async def serve_spa():
+        return FileResponse(os.path.join(static_dir, "index.html"))
+
+    # Catch-all for SPA routing (must be last)
+    @app.get("/{full_path:path}")
+    async def serve_spa_routes(full_path: str):
+        # Don't catch API routes
+        if full_path.startswith("api/") or full_path.startswith("health") or full_path.startswith("grove/"):
+            from fastapi import HTTPException
+            raise HTTPException(status_code=404, detail="Not found")
+
+        index_path = os.path.join(static_dir, "index.html")
+        if os.path.exists(index_path):
+            return FileResponse(index_path)
+
+        from fastapi import HTTPException
+        raise HTTPException(status_code=404, detail="Not found")