refactor(manager): retire project work on worktree removal

[boadij]

Fixes #225

Summary

• Retire only the matching project assignment and retained messages after an authoritative Herdr linked-worktree removal.
• Keep missing-worktree recovery nonterminal and preserve the Git branch.
• Remove Manager completion/discard controls superseded by worktree removal.

Validation

• Focused tests passed for Herdr, controller API, commands, extension contract, and smoke runner.
• npm run check: 805 passed, 1 skipped, 0 failed.
• npm run build and npm run package:audit passed.
• npm run smoke -- manager-recovery: scenario and cleanup passed.
• git diff --check passed.

[boadij]

External Review #1 follow-up is pushed in 0ceb99552e4357b701fcb665940d364cc498cf06.

• Removed the Manager/currentManager and session-ID gate: any eligible same-repository observer may retire only on authoritative Herdr removal. Repository/scope checks, both locks, and the expected-assignment-ID guard remain.
• Made the test socket portable: Windows uses a named pipe; Unix uses a short temporary socket path with cleanup in finally.
• Validation: focused controller test passed (95 tests); npm run check passed (805 passed, 1 skipped); npm run build passed; npm run package:audit passed (55 files); fresh manager-recovery smoke scenario and cleanup passed; git diff --check passed.

[boadij]

External Review #2 is resolved on rebased head 623844c756046c736cff84801be1675a436ce464.

• Retained the refactor(coordination): make managed Leads orchestration-first #224 orchestration-first Lead contract and delegation guidance.
• Retained refactor(manager): retire project work on worktree removal #226's nonterminal-settlement invariant and Herdr retirement authority; no complete/discard tools were added.
• The commands test retains the orchestration assertions and covers the nonterminal invariant.
• docs/concepts/delegation.md is unchanged from main.

Validation on the rebased head: npm run check passed (805 passed, 1 skipped); build and package:audit passed (55 files); git diff --check passed; focused tests passed (337 across commands, controller-api, extension-contract, herdr, and smoke-runner). The fresh manager-recovery smoke scenario and cleanup both passed. Final prettier . --write made no changes, and post-format check/diff-check passed.