Add pre-commit hooks for linting and formatting

Set up pre-commit framework with ruff (backend) and ESLint/Prettier/tsc
(frontend) hooks to catch issues locally before CI. Auto-format all
frontend files with Prettier to comply with the new check.

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

.pre-commit-config.yaml

@@ -0,0 +1,34 @@
+repos:
+  # Backend (Python) — ruff linting + formatting
+  - repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.15.0
+    hooks:
+      - id: ruff
+        args: [--fix]
+        files: ^backend/
+      - id: ruff-format
+        files: ^backend/
+
+  # Frontend (TypeScript/React) — local hooks using project node_modules
+  - repo: local
+    hooks:
+      - id: eslint
+        name: eslint
+        entry: npx eslint
+        language: system
+        files: ^frontend/src/.*\.(ts|tsx)$
+        pass_filenames: true
+
+      - id: prettier
+        name: prettier
+        entry: npx prettier --check
+        language: system
+        files: ^frontend/src/.*\.(ts|tsx|css|json)$
+        pass_filenames: true
+
+      - id: tsc
+        name: tsc
+        entry: bash -c 'cd frontend && npx tsc -b'
+        language: system
+        files: ^frontend/src/.*\.(ts|tsx)$
+        pass_filenames: false