fix(ci): drop --frozen in tradein test job (uv.lock is gitignored)

The #666 pytest gate ran `uv sync --frozen`, but tradein-mvp/backend/uv.lock
is gitignored → absent in a fresh CI checkout → 'Unable to find lockfile…
--frozen was provided' → test job failed → build+deploy skipped (deploy still
blocked after the PEP668 uv-install fix). Resolve from pyproject.toml instead
(uv sync, dev group included), matching the Dockerfile's `uv sync --no-dev`.

.forgejo/workflows/deploy-tradein.yml

@@ -69,7 +69,10 @@ jobs:
           echo "$HOME/.local/bin" >> "$GITHUB_PATH"
 
       - name: Sync deps (incl. dev group — pytest)
-        run: uv sync --frozen
+        # NB: tradein-mvp/backend/uv.lock is gitignored (see tradein-mvp/.gitignore),
+        # so --frozen can't work in CI (no lockfile in a fresh checkout). Resolve
+        # from pyproject.toml like the Dockerfile does (uv sync --no-dev there).
+        run: uv sync
 
       - name: Run pytest (tradein-mvp/backend)
         # DESELECT (2026-05): two pre-existing tests fail only in whole-suite