fix: use chokidar raw events as fallback for suppressed file changes

[graygilmore]

Summary

• Adds a raw event listener on chokidar as a transparent fallback to catch file changes that chokidar suppresses when mtime is unchanged (common with build tools on Linux/Windows)
• Uses a 100ms debounce: if chokidar's normal change fires within the window, the raw fallback is cancelled; if not, we trigger the handler ourselves
• Zero impact on macOS where FSEvents works reliably — the normal change always cancels the raw timeout

Problem

chokidar's _handleFile listener (nodefs-handler.js:369) compares mtimeMs and suppresses change events when mtime hasn't changed. Build tools that preserve timestamps cause silent misses on Linux/Windows.

How it works

1. chokidar emits a raw event unconditionally, even when the mtime check suppresses the change event
2. We start a 100ms timeout when a raw event fires
3. If chokidar's normal change fires within that window → cancel the timeout (normal path)
4. If the timeout expires (mtime unchanged, change suppressed) → trigger the handler ourselves
5. The existing handleFileUpdate computes MD5 checksums and only syncs when content changed, preventing redundant uploads even if both paths fire

Test plan

• New test: raw event triggers change handler when chokidar suppresses change
• New test: raw event is cancelled when chokidar change event fires (normal case)
• New test: duplicate raw events for the same path are deduplicated
• All 45 tests pass (42 existing + 3 new)

🤖 Generated with Claude Code

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	77.33%	14621/18908
🟡	Branches	70.91%	7252/10227
🟡	Functions	76.33%	3712/4863
🟡	Lines	78.83%	13823/17535

Test suite run success

3814 tests passing in 1474 suites.

Report generated by 🧪jest coverage report action from 2a3fcea