fix(#1367): project-local install uses flat gsd-<cmd>.md layout (fixes /gsd: colon namespace) (#1489)

* fix(#1367): project-local install uses flat gsd-<cmd>.md layout

Claude Code project-local installs now write command files as flat
gsd-<cmd>.md at .claude/commands/ level instead of commands/gsd/<cmd>.md
(subdirectory), so Claude Code registers /gsd-<cmd> (hyphen form)
matching hooks, statusline, and all cross-command references.

- capabilities/claude/capability.json: local destSubpath commands/gsd → commands
- bin/install.js else branch: flat gsd-<stem>.md loop with runtime rewrites
- bin/install.js uninstall (1c): remove flat files + legacy subdir cleanup
- bin/install.js writeManifest: record flat commands/gsd-<cmd>.md keys
- legacy migration: preserves dev-preferences.md across reinstall and uninstall
- gsd-core/bin/lib/capability-registry.cjs: regenerated
- 6 new regression tests (L0–L5) in bug-1367-*.test.cjs
- Updated E suite in bug-3683 + bug-1736, layout + surface + descriptor tests
- scripts/lint-regression-test-names.allowlist.json: grandfathered bug-1367 test

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(#1367): add issue reference to allow-test-rule comment

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/lint-regression-test-names.allowlist.json

@@ -2,6 +2,7 @@
   "bug-10-semver-policy-consolidation.test.cjs",
   "bug-130-finishinstall-opencode-testmode.test.cjs",
   "bug-131-release-tarball-smoke-explicit-home.test.cjs",
+  "bug-1367-claude-local-flat-command-layout.test.cjs",
   "bug-14-progress-auto-flag-dropped.test.cjs",
   "bug-167-query-meta-command.test.cjs",
   "bug-17-askuserquestion-option-cap.test.cjs",