fix: Add /profiles/me endpoint for session persistence

- AuthContext checks /profiles/me on mount to restore session
- Without this endpoint, users had to re-login on every refresh
- Returns current user's profile based on auth token

Issue: Session persistence broken

backend/routers/profiles.py

@@ -29,6 +29,20 @@ def get_pid(x_profile_id: Optional[str] = Header(default=None)) -> str:
     raise HTTPException(400, "Kein Profil gefunden")
 
 
+# ── Current User Profile ──────────────────────────────────────────────────────
+@router.get("/profiles/me")
+def get_current_profile(session=Depends(require_auth)):
+    """Get current user's profile (for auth check on refresh)."""
+    profile_id = session['profile_id']
+    with get_db() as conn:
+        cur = get_cursor(conn)
+        cur.execute("SELECT * FROM profiles WHERE id=%s", (profile_id,))
+        row = cur.fetchone()
+        if not row:
+            raise HTTPException(404, "Profil nicht gefunden")
+        return r2d(row)
+
+
 # ── Admin Profile Management ──────────────────────────────────────────────────
 @router.get("/profiles")
 def list_profiles(session=Depends(require_auth)):