fix(upgrade): remove hard chain depth cap for nightly delta upgrades

[BYK]

The MAX_CHAIN_DEPTH=10 limit silently rejected nightly delta upgrade chains
when >10 commits landed on main between the current and target versions (~2-3
days of normal development). This caused fallback to full binary downloads (~30 MB)
even when the total patch chain was much smaller.

The existing SIZE_THRESHOLD_RATIO=0.6 already guards against chains where cumulative
patch size exceeds 60% of the full binary — this is the meaningful cost/benefit check.
The hard depth limit was redundant for nightly and fired before the size check could run.

Changes

• Rename MAX_CHAIN_DEPTH → MAX_STABLE_CHAIN_DEPTH (stable keeps the limit since
  it also controls GitHub Releases per_page)
• Remove hard depth cap from resolveNightlyChain — nightly chains now rely solely on
  the size budget
• Add debug logging when chain resolution is rejected so --verbose reveals why delta
  was skipped

[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

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New Features ✨

• Add sentry schema command for API introspection by BYK in #437

Bug Fixes 🐛

• (upgrade) Remove hard chain depth cap for nightly delta upgrades by BYK in #444

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_{🤖 This preview updates automatically when you update the PR.}

[github-actions]

Codecov Results 📊

✅ 111 passed | Total: 111 | Pass Rate: 100% | Execution Time: 0ms

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	—
Failed Tests	—
Skipped Tests	—

✨ No test changes detected

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 1071 uncovered lines.
✅ Project coverage is 95.25%. Comparing base (base) to head (head).

Files with missing lines (1)

File	Patch %	Lines
delta-upgrade.ts	96.28%	⚠️ 25 Missing

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    95.11%    95.25%    +0.14%
==========================================
  Files          167       167         —
  Lines        22531     22542       +11
  Branches         0         0         —
==========================================
+ Hits         21430     21471       +41
- Misses        1101      1071       -30
- Partials         0         0         —

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Generated by Codecov Action

[BYK]

Addressed BugBot feedback: added MAX_NIGHTLY_CHAIN_DEPTH = 30 as a safety net against unbounded GHCR manifest fan-out. This matches the GHCR cleanup KEEP_COUNT (30 retained nightly tags), so every retained patch tag is usable while preventing runaway Promise.all bursts. The size budget (SIZE_THRESHOLD_RATIO = 0.6) remains the primary cost/benefit guard.

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