docs: strengthen tree API report guidance to prevent spurious diffs

[noencke]

Description

Strengthens documentation around handling unexpected API report diffs in @fluidframework/tree. The existing docs recommended per-package clean builds, but these are unreliable due to an incremental TypeScript bug that leaves stale artifacts in dependency packages. All relevant docs now prescribe a full root-level pnpm clean && pnpm build as the only reliable fix.

Also adds a note to the fluid-pr skill about the workaround for editing existing PR descriptions (write to a temp file for the user to copy-paste, since the agent lacks upstream write access).

Changes:

• CLAUDE.md / copilot-instructions.md: Add short "never hand-edit api.md" rule with pointer to tree-api-checks.md
• tree-api-checks.md: Rewrite phantom-diff section with explicit "golden rule", anti-pattern list, full root clean commands, and guidance to inform the user before starting long builds. Remove incorrect azure-client references and redundant cascade section (full build already covers aggregators).
• ci-readiness-check SKILL.md: Distinguish tree (needs root clean) from other packages (scoped clean OK); add never-hand-edit warning
• fluid-pr SKILL.md: Add section on updating existing PR descriptions via temp file

Reviewer Guidance

The review process is outlined on this wiki page.

Documentation-only change — no functional code affected.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates internal contributor/agent documentation to reduce spurious @fluidframework/tree API report diffs by steering folks toward reliable “full clean build” workflows and away from hand-editing generated artifacts.

Changes:

• Adds “never hand-edit *.api.md” guidance and pointers to tree-specific API diff troubleshooting docs.
• Reworks tree API diff troubleshooting instructions to emphasize root-level pnpm clean && pnpm build over scoped cleans.
• Updates CI readiness-check guidance to reflect the tree/aggregator incremental TypeScript nondeterminism behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
.github/copilot-instructions.md	Adds API report “generated artifact” rule + pointer to tree API checks doc.
.claude/CLAUDE.md	Mirrors the API report guidance for Claude instructions.
.claude/skills/ci-readiness-check/tree-api-checks.md	Reframes tree-specific API report troubleshooting around full clean builds and examples.
.claude/skills/ci-readiness-check/SKILL.md	Updates readiness-check workflow to prefer root clean/build for tree-related API diffs.
.claude/skills/fluid-pr/SKILL.md	Documents how to provide updated PR body text via a temp file for manual copy/paste.

[github-actions]

🔗 No broken links found! ✅

Your attention to detail is admirable.

linkcheck output

> fluid-framework-docs-site@0.0.0 ci:check-links /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test "npm run serve -- --no-open" 3000 check-links

1: starting server using command "npm run serve -- --no-open"
and when url "[ 'http://127.0.0.1:3000' ]" is responding with HTTP status code 200
running tests using command "npm run check-links"


> fluid-framework-docs-site@0.0.0 serve
> docusaurus serve --no-open

[SUCCESS] Serving "build" directory at: http://localhost:3000/

> fluid-framework-docs-site@0.0.0 check-links
> linkcheck http://localhost:3000 --skip-file skipped-urls.txt

Crawling...

Stats:
  279037 links
    1880 destination URLs
    2126 URLs ignored
       0 warnings
       0 errors