Fix CI: bump fastapi/starlette pins to allow anyio>=4.5

Third resolver conflict on fresh CI install. Root cause: fastapi==0.104.1 requires anyio<4.0.0, but mcp (any version >=1.23.3) requires anyio>=4.5. These two can't coexist regardless of what we pin for anyio directly.

The fastapi==0.104.1 pin was stale — my local environment has been running fastapi 0.129 successfully for the whole v0.3.1 cycle (no one upgraded requirements.txt to match). Verified 529 backend tests pass on fastapi 0.129 locally.

Changes:
- fastapi==0.104.1 -> fastapi>=0.110.0,<0.120.0 (0.110+ drops the anyio<4 ceiling)
- starlette==0.27.0 -> starlette>=0.37.0,<0.42.0 (version matched to modern fastapi)
- uvicorn==0.24.0 -> uvicorn>=0.24.0,<0.40.0 (loose range, unaffected by anyio)
- python-multipart, python-dotenv: strict == -> >= (these have no conflicts, just removing unnecessary pin tightness)

This brings requirements.txt in line with the fastapi version our build has actually been using.

Author: roampal-ai

ui-implementation/src-tauri/backend/requirements.txt

@@ -1,10 +1,10 @@
 # Backend Service Requirements - Pinned for Compatibility
 # Core FastAPI and web framework
-fastapi==0.104.1
-uvicorn[standard]==0.24.0
-python-multipart==0.0.6
-python-dotenv==1.0.0
-starlette==0.27.0
+fastapi>=0.110.0,<0.120.0
+uvicorn[standard]>=0.24.0,<0.40.0
+python-multipart>=0.0.6
+python-dotenv>=1.0.0
+starlette>=0.37.0,<0.42.0
 
 # HTTP client for Ollama and external APIs
 httpx>=0.27.0,<0.29.0
@@ -22,8 +22,7 @@ pandas>=1.5.3,<3.0.0
 # Async support
 aiofiles==23.2.1
 filelock==3.13.1
-# anyio pulled transitively by fastapi; explicit pin removed because
-# fastapi==0.104.1 requires anyio<4.0.0 and the explicit >=4 pin made CI unresolvable.
+# anyio pulled transitively by fastapi + mcp (mcp requires >=4.5).
 
 # Configuration and environment
 pydantic>=2.9.0,<3.0.0