fix: code-server respawn review follow-ups (from #583 Copilot review)

[sahil-noon]

Summary

PR #583 was merged before its Copilot review fixes were pushed, stranding the fix commit on the merged branch. This re-lands those three review fixes on top of main.

Changes

• respawnOutcome gains an explicit respawnFailed zero value — error paths no longer return a zero value that reads as "done" (Copilot comment on code_server.go:216)
• migrateForeignCodeServerSession no longer treats an unresolvable managed binary as "ours" — the no-anchor case now prints a note instead of silently skipping the migration check (code_server.go:277)
• daemon.CodeServerSessionCommand doc comment states the daemon-liveness gate obligation — callers must gate on daemon.IsRunning before calling (tmux probes on a dead socket birth a server) (codeserver.go:366)

[sahil-noon]

Added two production fixes observed on a real install attempt:

1. Extraction refused every real tarball — node_modules/.bin's up-and-back-down relative symlinks (.bin/esvalidate -> ../esprima/bin/esvalidate.js) hit the ../-prefix ban from the feat: Own the code-server Install #582 hardening. The lexical check is now containment against the link's resolved parent; the post-creation resolution check stays as the escape backstop. Regression test added with the exact reported shape, plus an env-gated manual test verified against the real 227MB v4.132.0 tarball.
2. Release resolve bound 10s → 30s — back-to-back context deadline exceeded on api.github.com observed before a third attempt succeeded.