feat(loop-worktree): expose public lock API

[shixi-li]

Summary

Expose the advisory lock coordinator through the supported
@cobusgreyling/loop-worktree/lock subpath, following the explicit follow-up
welcomed in #399.

Why

loop-sandbox currently reaches into
@cobusgreyling/loop-worktree/dist/lock.js. That private build path makes
consumers depend on package layout rather than a public contract. This PR
establishes the package contract without changing lock runtime behavior.

The loop-sandbox import migration is intentionally deferred until
loop-worktree@1.3.0 is published and #398 has settled, avoiding a
cross-package release dependency and overlapping changes.

Changes

• add root and ./lock conditional exports with declaration mappings
• retain ./dist/* and ./package.json compatibility exports
• add typesVersions support for classic TypeScript module resolution
• bump loop-worktree to 1.3.0, align the previously stale lockfile, and
  update the publish checklist
• document the public library imports
• run the existing lock suite through the public package self-reference
• add a packed, clean-consumer test covering root, public lock, legacy deep
  imports, and NodeNext/classic TypeScript resolution
• invoke npm portably in the consumer test and keep cleanup compatible with
  the full declared Node 18 range

Scope

This PR does not modify loop-sandbox, manifest concurrency, or the open #398
work.

Validation

• cd tools/loop-worktree && npm test — 32/32 passed
• cd tools/loop-audit && npm run build && node dist/cli.js ../.. — 100/100 L3
• git diff --check

Follow-up to #399.

[shixi-li]

Rebased this PR onto current main (081fca1) and marked it ready for review.

The rebase was conflict-free, and git range-diff confirms that the PR commits remain patch-equivalent. The scope is unchanged: the public loop-worktree/lock export, package export map, tests, and documentation.

Validation on the rebased head 52476ed:

• tools/loop-worktree: npm test — 32/32 passed.
• tools/loop: npm test — 10/10 passed.
• tools/loop-audit: npm run build — passed.
• node tools/loop-audit/dist/cli.js . — 100/100 (L3), passed.
• node tools/loop/dist/cli.js status . — passed.
• bash scripts/before-after-demo.sh — passed through all stages.
• node tools/loop/dist/cli.js doctor . reports the repository's existing Sync score of 90 and exits 1. I ran the same built CLI against a clean worktree at unmodified main; it produced the identical Sync warning and exit code, so this is not introduced by this PR.

This follows the maintainer's explicit invitation on #399 for a public loop-worktree/lock export. The broader loop-sandbox migration remains intentionally out of scope, as documented in the PR.

Ready for maintainer review.

[cobusgreyling]

Review

Clean package-contract PR for the advisory lock coordinator:

• Public @cobusgreyling/loop-worktree/lock export map + typesVersions
• Tests import via the public subpath; new pack/export test covers the contract
• README documents the stable entry point
• Version bump 1.2.0 → 1.3.0 + RELEASE_NOTES_DRAFT publish note
• Scope correctly defers loop-sandbox import migration

Merge. Thanks @shixi-li — good follow-up to #399.