Tier /submit-for-review outcomes and tighten WARNING/NOTE rubric

[sebastientaggart]

Tier review outcomes so clean and informational reviews auto-proceed, while genuinely actionable findings still surface a human decision moment. Also tightens the WARNING vs NOTE rubric so the reviewer disambiguates "informational" from "actionable but non-blocking" deliberately.

Tier classification (printed before any action so the routing is visible):

• clean — no findings → auto-merge.
• informational — [NOTE] only → auto-merge, NOTEs surfaced in confirmation, no prompt.
• needs-attention — [WARNING] present (no CRITICAL) → stop and ask: address now / follow up later / accept as-is.
• must-address — [CRITICAL] present → stop, return to coding.

Reviewer prompt changes (skills/github-agile/review-agent.md):

• New "sensitive-area gate" forces [CRITICAL] regardless of code quality when the PR touches auth, payments, secrets, production config, or destructive operations. This is intentionally always-on; the deferred per-project configurability is tracked in Make the reviewer's 'force CRITICAL on sensitive areas' rule configurable per project #174.
• Explicit semantic rubric for [WARNING] vs [NOTE] with three examples each. WARNING is now "non-blocking but actionable"; NOTE is "purely informational, no action implied." When in doubt, the reviewer is instructed to choose WARNING.
• NOTEs are exempt from the standalone-ticket-title phrasing rule (since they never become tickets).

Skill changes (skills/github-agile/submit-for-review.md):

• Step 8 reorganized into the four-tier classification above.
• Step 9 (follow-up issue offering) scoped to actionable findings only. NOTEs never become tickets. The "accept as-is" branch on needs-attention skips Step 9 entirely. The "follow up later" branch auto-creates issues for all WARNINGs without re-prompting.

Part of #167.

Closes #170

[sebastientaggart]

Review Summary

Verdict: APPROVE

Findings

• [NOTE] PR is documentation-only — modifies prompt/skill markdown files. Source-of-truth changes are in skills/github-agile/review-agent.md and skills/github-agile/submit-for-review.md; the .agents/, .claude/, .cursor/, and .gemini/ files are sync-generated mirrors with matching content and updated hashes, consistent with the project's sync convention.
• [NOTE] Tier classification, sensitive-area gate, and tightened WARNING vs NOTE rubric match what the PR description promises, and the Step 9 follow-up gating is updated coherently (NOTEs excluded from ticket creation, "accept as-is" branch skips Step 9, "follow up later" auto-creates without re-prompting).