ci: Set up Warden PR review

[gricha]

Add Warden automated code review for pull requests.

Rewrites warden.toml from the old [[triggers]] format to the current [[skills]] schema and adds a GitHub Actions workflow that runs getsentry/warden@v1 with the org GitHub App token for branded review comments.

Skills configured:

• notseer — bug finding on src/**/*.ts (excluding tests)
• security-review — security vulnerability scanning via getsentry/sentry-skills
• warden-lint-judge — commented out pending feat: multi-pass skill pipeline warden#144 (multi-pass pipeline with scope = "report")

Relies on org-level secrets: WARDEN_APP_ID, WARDEN_PRIVATE_KEY, WARDEN_ANTHROPIC_API_KEY (via the app token flow), and optional WARDEN_MODEL / WARDEN_SENTRY_DSN.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Workflow grants unnecessary contents: write permission

Medium Severity

The workflow declares contents: write at the top level, but a PR review workflow only needs to read repository contents and post review comments. Granting contents: write allows the workflow (and any actions it invokes, including the third-party getsentry/warden action) to push commits, create/delete branches, and modify repository contents. Narrowing this to contents: read follows the principle of least privilege and limits blast radius if any action is compromised.