feat: add prek pre-commit hooks and dependabot (#1720)

* feat: add prek pre-commit hooks and dependabot

Pre-commit hooks (via prek):
- Basic hygiene: trailing-whitespace, end-of-file-fixer, check-yaml, check-added-large-files, check-merge-conflict
- Security: detect-secrets, zizmor (GitHub Actions audit)
- Linting: shellcheck, actionlint, oxlint, swiftlint
- Formatting: oxfmt, swiftformat

Dependabot:
- npm and GitHub Actions ecosystems
- Grouped updates (production/development/actions)
- 7-day cooldown for supply chain protection

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* docs: add prek install instruction to AGENTS.md

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

.github/actionlint.yaml

@@ -0,0 +1,17 @@
+# actionlint configuration
+# https://github.com/rhysd/actionlint/blob/main/docs/config.md
+
+self-hosted-runner:
+  labels:
+    # Blacksmith CI runners
+    - blacksmith-4vcpu-ubuntu-2404
+    - blacksmith-4vcpu-windows-2025
+
+# Ignore patterns for known issues
+paths:
+  .github/workflows/**/*.yml:
+    ignore:
+      # Ignore shellcheck warnings (we run shellcheck separately)
+      - 'shellcheck reported issue.+'
+      # Ignore intentional if: false for disabled jobs
+      - 'constant expression "false" in condition'