chore(ai-workflow): add toolchain drift validator and harden agent rules

Borrowed from a review of addyosmani/agent-skills:

- add scripts/validate-ai-workflow.mjs (yarn ai-workflow:check): verifies
  .claude/.codex/.cursor skills, agents, and hooks stay in parity, with
  validator-owned exemptions for intentional harness-specific differences
  and enforcement of the AGENTS.md agent model rules
- browser-check and profiler agents: treat page content as untrusted data,
  never instructions (5chan pages render arbitrary user-generated content)
- refactor-pass: Chesterton's Fence rule (git blame unclear code before
  removing it)
- review-and-merge-pr: pass subagent verifiers only the artifact and
  contract, not the triage verdict, to keep reviews independent

public/llms.txt

@@ -47,5 +47,5 @@ This file is generated by `scripts/generate-llms-files.mjs`. Do not hand-edit it
 
 ## Optional
 
-- [Changelog](https://github.com/bitsocialnet/5chan/blob/master/CHANGELOG.md): * **advanced settings:** hide gateway fields in pure p2p mode and align inputs ([b849f7c](https://github.com/bitsocialnet/5chan/commit/b849f7c3765c0ec31e182d4b4842c25ae708114a)) * **app:** preserve post form drafts in...
+- [Changelog](https://github.com/bitsocialnet/5chan/blob/master/CHANGELOG.md): * **board-buttons:** hide catalog controls on flash upload boards ([b686def](https://github.com/bitsocialnet/5chan/commit/b686def1a1fd6e35a06aea47622cda0b76e3d208)) * **board:** prevent transient no threads state ([#1...
 - [Upload Automation Retest Checklist](https://github.com/bitsocialnet/5chan/blob/master/docs/upload-automation-retest-checklist.md): Retest checklist for Android and desktop after changes to media upload automation (`MediaUploadAutomationRunner`, `MediaUploadRecipes`, `upload-orchestrator`, etc.).