feat: subdirectory manifests + npm-valid version mirror (#2531)

Two gaps in gstack-version-bump's manifest handling, resolved to the wave
plan's version-tooling end-state spec (decision 11):

1. Subdirectory manifests. A repo whose only Node package lives in web/,
   app/, or frontend/ has no ROOT package.json, so join(cwd,
   "package.json") reported pkgExists:false and every bump silently wrote
   VERSION alone — leaving the manifest to be bumped by hand, which is
   exactly the drift this tool exists to prevent, in the one layout where
   it silently did nothing. All three subcommands now resolve the
   manifest as --package-json-path → .gstack/package-json-path →
   ./package.json (mirroring resolveVersionPath).

2. npm-valid mirror. VERSION is 4-digit MAJOR.MINOR.PATCH.MICRO; npm's
   semver is 3-component and rejects a fourth, so mirroring the raw form
   breaks `npm ci` in any repo npm actually manages. The manifest and its
   lockfiles now carry the npm-valid 3-digit translation (1.67.0.0 →
   1.67.0) via npmVersion() in lib/version-source.ts. VERSION stays the
   4-digit source of truth. classify judges drift against the TRANSLATED
   form — a correctly-synced `0.1.25` no longer reads as eternal drift
   against `0.1.25.0` — and grandfathers the pre-v1.67 1:1 four-digit
   mirror as in-sync (flagging it DRIFT_UNEXPECTED would hard-stop /ship
   on every existing repo on upgrade day; the next write migrates the
   manifest to the translated form). Lockfiles are synced beside the
   resolved manifest — including beside a pinned JSON version-path — and
   only when they already exist.

classify output gains pkgPath and expectedPkgVersion for observability;
write/repair report packageJsonPath + packageJsonVersion. The /ship Step
12 prose (ship/SKILL.md.tmpl) documents the resolution chain and the
translation; SKILL.md files regenerated and ship golden fixtures
refreshed in this commit.

Tests: subdirectory pin + --package-json-path override, translated-form
classify (FRESH/ALREADY_BUMPED, no false drift), grandfathered 1:1
mirror, genuine divergence still drifts, repair to the npm-valid form
(33 pass in test/gstack-version-bump.test.ts; 526 pass across the five
affected files including goldens and parity).

Re-derived from PR #2531 by @CarringtonCreative on top of the 3-digit/
JSON version-source work, under decision 11 (which resolves the PR's
lockfile-gated translation in favor of an unconditional npm-valid
mirror).

Co-authored-by: Carrington Dennis <carrdenn3@gmail.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ship/SKILL.md

@@ -1108,7 +1108,7 @@ stay agent judgment; the slot pick stays `gstack-next-version`.
    ```bash
    bun run ~/.claude/skills/gstack/bin/gstack-version-bump write --version "$NEW_VERSION"
    ```
-   The CLI validates the 4-digit `MAJOR.MINOR.PATCH.MICRO` pattern and writes **both** VERSION and package.json. On a half-write (VERSION written, package.json failed) it exits 3 — re-run, and classify will report DRIFT_STALE_PKG for `repair` to fix.
+   The CLI validates the version pattern (4-digit `MAJOR.MINOR.PATCH.MICRO`; 3-digit for repos whose pinned version source uses plain semver) and writes VERSION, the manifest, and the manifest's npm lockfiles (`package-lock.json` / `npm-shrinkwrap.json`) when they already exist — never created. The manifest is resolved as `--package-json-path` → `.gstack/package-json-path` → `./package.json`, so a repo whose only Node package lives in a subdirectory (`web/`, `app/`) is covered by a one-line pin instead of silently getting a VERSION-only bump. npm rejects 4-component versions, so the manifest and lockfiles carry the npm-valid 3-digit translation (`1.67.0.0` → `1.67.0`); VERSION stays the 4-digit source of truth and classify judges drift against the translated form. On a half-write it exits 3 — re-run, and classify will report DRIFT_STALE_PKG for `repair` to fix.
 
 5. **Record the release decision** (durable cross-session memory). The bump level is a real decision the next session should not re-derive blind:
    ```bash

ship/SKILL.md.tmpl

@@ -201,7 +201,7 @@ stay agent judgment; the slot pick stays `gstack-next-version`.
    ```bash
    bun run ~/.claude/skills/gstack/bin/gstack-version-bump write --version "$NEW_VERSION"
    ```
-   The CLI validates the 4-digit `MAJOR.MINOR.PATCH.MICRO` pattern and writes **both** VERSION and package.json. On a half-write (VERSION written, package.json failed) it exits 3 — re-run, and classify will report DRIFT_STALE_PKG for `repair` to fix.
+   The CLI validates the version pattern (4-digit `MAJOR.MINOR.PATCH.MICRO`; 3-digit for repos whose pinned version source uses plain semver) and writes VERSION, the manifest, and the manifest's npm lockfiles (`package-lock.json` / `npm-shrinkwrap.json`) when they already exist — never created. The manifest is resolved as `--package-json-path` → `.gstack/package-json-path` → `./package.json`, so a repo whose only Node package lives in a subdirectory (`web/`, `app/`) is covered by a one-line pin instead of silently getting a VERSION-only bump. npm rejects 4-component versions, so the manifest and lockfiles carry the npm-valid 3-digit translation (`1.67.0.0` → `1.67.0`); VERSION stays the 4-digit source of truth and classify judges drift against the translated form. On a half-write it exits 3 — re-run, and classify will report DRIFT_STALE_PKG for `repair` to fix.
 
 5. **Record the release decision** (durable cross-session memory). The bump level is a real decision the next session should not re-derive blind:
    ```bash