Align repo config with global development standards

- Add missing tsconfig strictness flags (noUncheckedIndexedAccess,
  exactOptionalPropertyTypes, noImplicitOverride,
  noPropertyAccessFromIndexSignature) and fix all resulting type errors
- Replace ESLint/Prettier with oxlint 1.48.0 and oxfmt 0.33.0
- Pin all frontend and backend dependencies to exact versions
- Pin GitHub Actions to SHA hashes with persist-credentials: false
- Fix CI Python version mismatch (3.12 -> 3.14) and ruff target-version
- Add vitest 4.0.18 with jsdom environment for frontend testing
- Add ty 0.0.17 for Python type checking (non-blocking in CI)
- Add actionlint and zizmor CI job for workflow linting and security audit
- Add Dependabot config for npm, pip, and github-actions
- Update CLAUDE.md and pre-commit hooks to reflect new tooling
- Ignore Claude Code sandbox artifacts in gitignore

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

.github/workflows/ci.yml

@@ -22,21 +22,45 @@ jobs:
   backend-lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
         with:
-          python-version: "3.12"
-      - run: pip install ruff
+          persist-credentials: false
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065  # v5.6.0
+        with:
+          python-version: "3.14"
+      - run: pip install ruff ty
       - name: Check linting
         run: ruff check backend/
       - name: Check formatting
         run: ruff format --check backend/
+      - name: Type check
+        run: ty check backend/src/
+        continue-on-error: true
+
+  actions-lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
+        with:
+          persist-credentials: false
+      - name: Install actionlint
+        run: |
+          curl -sL https://github.com/rhysd/actionlint/releases/latest/download/actionlint_linux_amd64.tar.gz | tar xz
+          sudo mv actionlint /usr/local/bin/
+      - name: Lint GitHub Actions
+        run: actionlint
+      - name: Install zizmor
+        run: pip install zizmor
+      - name: Audit GitHub Actions security
+        run: zizmor .github/workflows/
 
   frontend-lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-node@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
+        with:
+          persist-credentials: false
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020  # v4.4.0
         with:
           node-version: "24"
       - name: Install dependencies
@@ -46,7 +70,7 @@ jobs:
         run: npm run lint
         working-directory: frontend
       - name: Check formatting
-        run: npx prettier --check "src/**/*.{ts,tsx,css,json}"
+        run: npx oxfmt --check "src/"
         working-directory: frontend
       - name: Type check
         run: npx tsc -b