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>

tests/runtime-artifact-layout.test.cjs

@@ -37,7 +37,7 @@ describe('resolveRuntimeArtifactLayout — claude local', () => {
     assert.strictEqual(layout.configDir, FAKE_DIR);
     assert.strictEqual(layout.kinds.length, 2);
     assert.strictEqual(layout.kinds[0].kind, 'commands');
-    assert.strictEqual(layout.kinds[0].destSubpath, 'commands/gsd');
+    assert.strictEqual(layout.kinds[0].destSubpath, 'commands'); // #1367: flat gsd-<cmd>.md layout
     assert.strictEqual(layout.kinds[0].prefix, 'gsd-');
     assert.strictEqual(typeof layout.kinds[0].stage, 'function');
     assert.strictEqual(layout.kinds[1].kind, 'agents');