Fix send request 500: revert to naive datetime.now() per project contract

The QA fix incorrectly changed datetime.now() to datetime.now(timezone.utc),
but the DB uses TIMESTAMP WITHOUT TIME ZONE (naive). Passing a tz-aware
datetime to a naive column causes asyncpg DataError. Also removes the
temporary diagnostic wrapper and builds response before commit.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/routers/connections.py

@@ -10,7 +10,7 @@ Security:
 """
 import asyncio
 import logging
-from datetime import date as date_type, datetime, timedelta, timezone
+from datetime import date as date_type, datetime, timedelta
 
 from fastapi import APIRouter, BackgroundTasks, Depends, HTTPException, Path, Query, Request
 from sqlalchemy import delete, select, func, and_, update
@@ -131,16 +131,6 @@ async def send_connection_request(
     current_user: User = Depends(get_current_user),
 ):
     """Send a connection request to another user."""
-    try:
-        return await _send_request_impl(body, request, background_tasks, db, current_user)
-    except HTTPException:
-        raise
-    except Exception as exc:
-        logger.error("send_connection_request UNHANDLED: %s", exc, exc_info=True)
-        raise HTTPException(status_code=500, detail=f"DEBUG: {type(exc).__name__}: {exc}")
-
-
-async def _send_request_impl(body, request, background_tasks, db, current_user):
     # Resolve target
     result = await db.execute(
         select(User).where(User.umbral_name == body.umbral_name)
@@ -194,7 +184,7 @@ async def _send_request_impl(body, request, background_tasks, db, current_user):
         raise HTTPException(status_code=409, detail="A pending request already exists")
 
     # Per-receiver cap: max 5 pending requests within 10 minutes
-    ten_min_ago = datetime.now(timezone.utc) - timedelta(minutes=10)
+    ten_min_ago = datetime.now() - timedelta(minutes=10)
     pending_count = await db.scalar(
         select(func.count())
         .select_from(ConnectionRequest)
@@ -388,7 +378,7 @@ async def _respond_to_request_inner(
     db: AsyncSession,
     current_user: User,
 ) -> RespondAcceptResponse | RespondRejectResponse:
-    now = datetime.now(timezone.utc)
+    now = datetime.now()
 
     # Atomic update — only succeeds if status is still 'pending' and receiver is current user
     result = await db.execute(
@@ -575,7 +565,7 @@ async def cancel_request(
     current_user: User = Depends(get_current_user),
 ):
     """Cancel an outgoing connection request. Atomic via UPDATE...WHERE status='pending'."""
-    now = datetime.now(timezone.utc)
+    now = datetime.now()
 
     # Atomic update — only succeeds if sender is current user and status is still pending
     result = await db.execute(