chore: add pre-commit ruff hook with auto-fix

- scripts/hooks/pre-commit: runs ruff --fix for root and web/ (matching CI)
  and re-stages any auto-fixed files so they land in the commit
- Makefile: add install-hooks target (run once after clone)
- pyproject.toml: exclude web/ from root ruff (web has its own config)
- Fix remaining import sort warnings caught by the new hook

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

scripts/hooks/pre-commit

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Pre-commit hook: ruff lint + auto-fix.
+# Install: make install-hooks
+set -euo pipefail
+
+REPO_ROOT="$(git rev-parse --show-toplevel)"
+RUFF="$REPO_ROOT/.venv/bin/ruff"
+
+if [[ ! -x "$RUFF" ]]; then
+    echo "pre-commit: ruff not found at $RUFF — run 'uv sync' first" >&2
+    exit 1
+fi
+
+echo "→ ruff check (root)"
+"$RUFF" check --fix "$REPO_ROOT"
+
+echo "→ ruff check (web/src web/tests)"
+"$RUFF" check --fix "$REPO_ROOT/web/src" "$REPO_ROOT/web/tests" \
+    --config "$REPO_ROOT/web/pyproject.toml"
+
+# Re-stage any files ruff fixed so they land in the commit.
+git diff --name-only | xargs -r git add