Fix watcher stale root cleanup

[pcristin]

Summary

• Track consecutive missing project roots in the watcher.
• Preserve projects through transient missing-root checks, then prune after three consecutive misses.
• Delete cached project DB/WAL/SHM files when sustained absence is confirmed.
• Add a regression test covering transient miss preservation and sustained cleanup.

Fixes #286.

Validation

• make -f Makefile.cbm build/c/test-runner passed.
• git diff --check passed.

[pcristin]

Damn, got a lucky number unintentionally xD

[DeusData]

Huge thanks for opening this PR and for the work you put into it.

The maintainer shop is currently full, so this may sit for a bit before it gets a proper review. We will come back to this as soon as possible with real feedback; I wanted to make sure it did not sit unacknowledged in the meantime.

[DeusData]

Thanks for the watcher cleanup. Please refresh the branch/title so generated/session naming is removed from the PR metadata and merge commit message. The non-merge commits appear DCO-signed, but if CI flags the merge commit, rebasing onto current main should clear it.

[pcristin]

@DeusData
By renaming PR branch, this PR was closed. Did all of what you asked and opened a new one: #738
Hope, It's okay