fix(push-hook): retry MR commits fetch to handle GitLab async race condition

[sylvaincombes]

Problem

When Homer receives a push hook, it filters the pushed commits by cross-referencing the GitLab MR commits API (to remove rebase noise). Because GitLab updates MR content asynchronously, the just-pushed commit is sometimes absent from the API response at the time Homer fetches it.

Flow:

1. A commit is pushed
2. Homer receives the hook almost instantly and fetches the MR commits
3. The commit isn't there yet → filtered out → no reviews left → Homer returns 204 and posts nothing (no error log, invisible)

Fix

Add a waitForMergeRequestCommits utility that polls the MR commits endpoint (up to 5 s, 1 s intervals) until at least one of the pushed commits appears, then falls back to a final fetch on timeout.

This follows the same pattern as the existing waitForReleasePipeline utility.

Changes

• src/review/commands/share/utils/waitForMergeRequestCommits.ts — new polling utility
• src/review/commands/share/hookHandlers/pushHookHandler.ts — use the new utility instead of a direct fetch
• __tests__/review/pushHook.test.ts — update mock to return a matching commit (the "no related review" test was asserting on the wrong layer; the 204 comes from no review in DB, not from empty commits)

[sylvaincombes]

Closing — opened prematurely, still iterating.

[codecov]

Codecov Report

❌ Patch coverage is 77.27273% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.12%. Comparing base (9315d06) to head (47b117c).

Files with missing lines	Patch %	Lines
...commands/share/utils/waitForMergeRequestCommits.ts	72.22%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #173      +/-   ##
==========================================
- Coverage   89.29%   89.12%   -0.17%     
==========================================
  Files         104      105       +1     
  Lines        2269     2289      +20     
  Branches      440      441       +1     
==========================================
+ Hits         2026     2040      +14     
- Misses        230      236       +6     
  Partials       13       13              

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