fix: remove pre-commit step — handled by pre-commit.ci now

pre-commit.ci runs on all PRs automatically. No need to duplicate
in the test workflow. Also pre-commit isn't in backend uv deps.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: abhizipstack

.github/workflows/core-backend-tests.yaml

@@ -36,17 +36,7 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
 
-      - name: Cache pre-commit hooks
-        uses: actions/cache@v4
-        if: github.ref != 'refs/heads/main'
-        with:
-          path: ~/.cache/pre-commit
-          key: ${{ runner.os }}-pre-commit-${{ hashFiles('.pre-commit-config.yaml') }}
-
-      - name: Check pre-commit
-        if: github.ref != 'refs/heads/main'
-        working-directory: .
-        run: uv run --directory backend pre-commit run --all-files
+      # pre-commit checks handled by pre-commit.ci
 
       - name: Run tests
         run: |