Rename to resolve the worktree-allocator filename collision

[JSONbored]

Context

src/miner/worktree-allocator.ts (gittensory-engine, pure git-worktree path/branch naming and retention policy) and lib/worktree-allocator.js (gittensory-miner, SQLite-backed slot leasing and PID-liveness-based orphan reclaim) share the same filename while doing genuinely different jobs. This is a minor but real source of confusion for anyone reasoning about the engine/miner split, especially for hosted-service planning where the two modules' very different portability (one is pure and reusable, the other is single-machine PID-coupled) matters.

Dependencies

None — independently shippable rename.

Requirements

1. Rename one of the two files so the split is legible at a glance — e.g. the engine-side pure planner to src/miner/worktree-plan.ts, keeping lib/worktree-allocator.js's name since it's the one that actually allocates/leases slots.
2. Update every import and reference to the renamed file/exports.
3. Out of scope: no behavior change to either module.

Deliverables / Acceptance Criteria

• One of the two worktree-allocator files renamed, with no functional change
• No file in the repo imports the old path
• Existing test suites for both files pass unchanged under their new name(s)

Test Coverage Requirements

Pure rename with no behavior change — existing test coverage carries over unchanged (rename the test file(s) to match).

Expected Outcome

The engine/miner reuse boundary reads clearly from filenames alone, without requiring prior context to know which worktree-allocator is pure and which is SQLite-backed.

Links & Resources

• packages/gittensory-engine/src/miner/worktree-allocator.ts
• packages/gittensory-miner/lib/worktree-allocator.js
• Relates to Miner Wave 5 (Epic: Miner Wave 5 — Rent-a-Loop #4778) and AMS Cloud Readiness (feat(mcp): detect stale installs and API compatibility in doctor and status #28) — identified while scoping the engine/miner reuse boundary.

[linear-code]

JSO-3882