Refactor SDK-first architecture seams (#3316)

* refactor: tighten sdk-first architecture seams

Refs #3312

* refactor: finish state document seam cleanup

Refs #3312

* test: harden minimal install cleanup assertion

* ci: support sdk-scoped package lock

* fix(3316): restore root package-lock.json and align changeset pr ref

Reverts dec57a83 ("ci: support sdk-scoped package lock") and restores
the root package-lock.json that c249d34d deleted. The deletion was the
wrong direction:

- The root package.json declares its own runtime and dev deps
  (@anthropic-ai/claude-agent-sdk, ws, c8). Without a root lockfile,
  `npm install --no-package-lock` resolves whatever satisfies semver at
  install time — CI today and CI in six months can install different
  transitive trees, defeating reproducibility.
- The lockfile has been part of every release on this repo (long
  history on main); removing it loses the npm audit / Dependabot
  target without compensating benefit.
- The CI workaround pattern (cache-dependency-path: sdk/package-lock.json
  + `npm install --no-package-lock`) papered over the symptom rather
  than fix the cause.

Also fix the changeset pr: from 3312 (issue) to 3316 (PR). CONTEXT.md
flags this exact failure mode as a recurring CodeRabbit finding.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix: address coderabbit review findings

* fix: close remaining coderabbit threads

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.changeset/3312-sdk-first-architecture-seams.md

@@ -0,0 +1,5 @@
+---
+type: Changed
+pr: 3316
+---
+Tighten SDK-first architecture seams across planning path projection, workstream inventory, STATE.md transforms, and CJS command routing. Shared CJS/SDK helpers now reduce drift, and STATE.md progress projection preserves curated wider aggregates without hiding real disk-derived progress.