feat(#607): rebuild get-shit-done-cc → gsd-core migration (per-package cache + installer auto-cleanup + --dry-run) (#611)

* feat(#607): rebuild get-shit-done-cc → gsd-core migration

Leftover get-shit-done-cc installs poisoned the shared update cache,
causing a permanent false "update available". Rebuild the migration so a
stale old install is both harmless and actively removed.

- Per-package update cache filename (gsd-update-check-<slug>.json) in the
  shared ~/.cache/gsd dir, single-sourced via package-identity; writers
  stamp package_name and readers reject foreign/absent lineage. Multi-
  runtime visibility preserved (same shared dir + filename across runtimes).
- New get-shit-done/bin/lib/legacy-cleanup.cjs seam: detects code-file
  references to the old package + the legacy fixed-name cache across home
  runtime dirs; installer auto-cleans on every install; --dry-run previews
  and mutates nothing. User hooks and dev-preferences are never touched.
- update.md cache-clear globs gsd-update-check*.json across ALL supported
  runtimes (adds cursor/windsurf/augment/trae/qwen/hermes/codebuddy/cline).
- Fix worker MODULE_NOT_FOUND post-install (ship managed-hooks-registry.cjs
  + degrade gracefully) so the per-package cache is always written.
- Diataxis how-to: docs/cleanup-get-shit-done-cc.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#607): add changeset for PR #611

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(#607): set USERPROFILE alongside HOME in dry-run install test for Windows

os.homedir() reads USERPROFILE on win32, so HOME-only isolation let the
spawned installer scan the real runner home on windows-latest. Set both.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

tests/bug-2784-update-cache-clear-path.test.cjs

@@ -71,12 +71,12 @@ describe('bug-2784: update.md cache-clear covers shared cache path', () => {
     }
 
     const sharedCacheClearCmds = bashLines.filter(
-      (line) => /^rm\b/.test(line) && line.includes('.cache/gsd/gsd-update-check.json')
+      (line) => /^rm\b/.test(line) && line.includes('.cache/gsd/gsd-update-check') && line.includes('*.json')
     );
     assert.ok(
       sharedCacheClearCmds.length > 0,
       [
-        'run_update step bash blocks must include an `rm` command targeting .cache/gsd/gsd-update-check.json.',
+        'run_update step bash blocks must include an `rm` command targeting .cache/gsd/gsd-update-check*.json (glob form clearing legacy + per-package variants).',
         `Bash lines found: ${JSON.stringify(bashLines)}`,
       ].join('\n')
     );