fix(browse): report lock acquisition errors

[jbetala7]

Fixes #1084

Summary

• Treat only EEXIST from the browse server lock open as normal lock contention.
• Log unexpected lock open, holder-read, and stale-lock removal errors with the error code, lock path, and message before returning null.
• Retry cleanly if the lock disappears between the failed exclusive open and holder-PID read.
• Add focused coverage for lock diagnostics, live-lock silence, and stale-lock reacquisition.

Collision checks

• Searched open PRs by #1084, acquireServerLock, lock contention, EEXIST, and browse/src/cli.ts.
• Re-ran the same search after a fresh origin/main fetch immediately before pushing.
• No canonical or overlapping PR was found.

Testing

• bun test browse/test/cli-lock.test.ts browse/test/cli-supervisor.test.ts browse/test/cli-setsid-daemonize.test.ts
• git diff --check HEAD~1..HEAD
• git merge-tree --write-tree HEAD origin/main