chore: add pre-commit hook to catch lint errors before push

Adds ruff pre-commit hook that auto-fixes and formats on every commit,
preventing lint CI failures from reaching GitHub.

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

.pre-commit-config.yaml

@@ -0,0 +1,7 @@
+repos:
+  - repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.11.4
+    hooks:
+      - id: ruff
+        args: [--fix]
+      - id: ruff-format

requirements-dev.txt

@@ -10,6 +10,7 @@ pytest-mock>=3.15.1
 ruff>=0.1.0
 black>=23.0.0
 mypy>=1.0.0
+pre-commit>=3.0.0
 
 # Type stubs
 types-flask>=1.1.0