ci: Exempt private repositories from approval gate

[idy]

Closes #51

Summary

• Read the calling PR's base repository private flag from GitHub's trusted pull-request API response.
• Keep the 5,000,000-byte binary-aware admin approval gate for public callers; skip that gate for private callers.
• Continue enforcing the 100,000,000-byte hard limit for every caller. Unknown privacy fails closed as public.
• Cover private/public behavior in the diff-preparation tests and document the policy.

GizClaw/h6infra PR #4 is private and has an 18,621,002-byte binary-aware patch; after this policy is released, it should proceed without admin size approval.

Validation

• node .github/scripts/pr-review/test.mjs
• node .github/scripts/review-request/test.mjs
• node .github/scripts/pr-readiness/test.mjs
• node .github/scripts/issue-review/test.mjs
• actionlint -ignore 'property "workflow_(repository|sha)" is not defined' .github/workflows/*.yml
• git diff --check

[github-actions]

✅ OpenAI PR Review: PASS

Conclusion: Ready from the OpenAI review perspective. PR format, linked Issue design, and code/plan conformance passed with no actionable findings.

Review checks

Check	Result
PR format	✅ PASS
Issue design	✅ PASS
Code & plan conformance	✅ PASS

Scope: 86cbea3ab0 · 5e46add2aa..86cbea3ab0 · full · 1 diff chunk

Usage: 58s · 341,097 tokens · 82.3% cache hit · credits unavailable

Summary

The complete diff conforms to Issue #51’s plan. The single completed code review found no actionable issues or plan-conformance blockers.

Review metadata

• Commit: 86cbea3ab0
• Range: 5e46add2aa..86cbea3ab0
• Mode: full
• Diff chunks: 1
• Model: gpt-6-sol
• Reasoning effort: low
• Session: repo-1309321116-pr-52-v2
• Generation: 766d8acbbe26e28d3b3e82419203797bab2354330e457e64d3901b628bd17344
• Evidence: 87c44dc88b5eabfeac61abd16f69cad96d59288bfa71ae2405863daf29ac119b

Totals

• Input: 338,792
• Cached input: 278,929
• Cache write: 58,911
• Output: 2,305
• Reasoning: 282
• Total: 341,097
• Estimated credits: unavailable for this model

Token and cache details

Stage	Mode	Target	Time	Input	Cached	Hit	Output	Total	Credits
pr	deterministic	format rules	0s	0	0	0.0%	0	0	N/A
pr	full	pr	13s	43,189	27,758	64.3%	415	43,604	N/A
issue	full	Issue #51	16s	77,151	69,271	89.8%	731	77,882	N/A
code	full	chunk 1/1	17s	113,221	80,619	71.2%	786	114,007	N/A
code	full	aggregate	12s	105,231	101,281	96.2%	373	105,604	N/A