feat: add pre-commit hooks for linting

- Add .pre-commit-config.yaml with ruff and black hooks
- Add pre-commit git hook script as fallback
- Add pre-commit to requirements-dev.txt

Running 'pre-commit install' will auto-lint on every commit.

.pre-commit-config.yaml

@@ -0,0 +1,26 @@
+# Pre-commit hooks for vault-dash
+# Install: pip install pre-commit && pre-commit install
+repos:
+  # Ruff - fast Python linter
+  - repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.11.2
+    hooks:
+      - id: ruff
+        args: [--fix, --exit-non-zero-on-fix]
+        files: ^(app|tests|scripts)/
+
+  # Black - Python formatter
+  - repo: https://github.com/psf/black
+    rev: 25.1.0
+    hooks:
+      - id: black
+        files: ^(app|tests|scripts)/
+
+  # Type checking with mypy (optional, slower)
+  # Uncomment to enable:
+  # - repo: https://github.com/pre-commit/mirrors-mypy
+  #   rev: v1.15.0
+  #   hooks:
+  #     - id: mypy
+  #       args: [--ignore-missing-imports]
+  #       files: ^app/