fix(deploy): bind to IPv6 and add root endpoint for Railway

Author: dkhoid

src/docchat/api.py

@@ -164,6 +164,12 @@ class ErrorResponse(BaseModel):
 # ── Endpoints ─────────────────────────────────────────────────────────────────
 
 
+@app.get("/", include_in_schema=False)
+async def root():
+    from fastapi.responses import RedirectResponse
+    return RedirectResponse(url="/docs")
+
+
 @app.get("/health", response_model=HealthResponse)
 async def health():
     store = _get_store()

src/docchat/server.py

@@ -6,7 +6,7 @@
 def main() -> None:
     import uvicorn
 
-    host = os.environ.get("DOCCHAT_HOST", "0.0.0.0")
+    host = os.environ.get("DOCCHAT_HOST", "::")
     # Railway (và các Cloud PaaS khác) tự động cấp phát cổng qua biến PORT
     port_str = os.environ.get("PORT") or os.environ.get("DOCCHAT_PORT", "8000")
     port = int(port_str)