Align repo config with global development standards

- Add missing tsconfig strictness flags (noUncheckedIndexedAccess,
  exactOptionalPropertyTypes, noImplicitOverride,
  noPropertyAccessFromIndexSignature) and fix all resulting type errors
- Replace ESLint/Prettier with oxlint 1.48.0 and oxfmt 0.33.0
- Pin all frontend and backend dependencies to exact versions
- Pin GitHub Actions to SHA hashes with persist-credentials: false
- Fix CI Python version mismatch (3.12 -> 3.14) and ruff target-version
- Add vitest 4.0.18 with jsdom environment for frontend testing
- Add ty 0.0.17 for Python type checking (non-blocking in CI)
- Add actionlint and zizmor CI job for workflow linting and security audit
- Add Dependabot config for npm, pip, and github-actions
- Update CLAUDE.md and pre-commit hooks to reflect new tooling
- Ignore Claude Code sandbox artifacts in gitignore

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

.gitignore

@@ -67,3 +67,28 @@ temp/
 
 # Local config overrides
 *.local
+
+# Claude Code sandbox artifacts
+/HEAD
+/config
+/hooks
+/objects
+/refs
+/frontend/HEAD
+/frontend/config
+/frontend/hooks
+/frontend/objects
+/frontend/refs
+/.gitmodules
+/.gitconfig
+/.bash_profile
+/.bashrc
+/.profile
+/.zprofile
+/.zshrc
+/.ripgreprc
+/.mcp.json
+/.claude/agents
+/.claude/commands
+/.claude/skills
+/frontend/.claude/