feat(#785): write .cursor/commands/ Cursor 1.6 slash-command surface (#805)

* feat(#785): write .cursor/commands/ as Cursor 1.6 slash-command surface

Cursor 1.6 (released 2025-09-12) introduced plain-markdown slash commands
in `.cursor/commands/<name>.md` — no frontmatter, invocable via `/` in the
Agent input. GSD previously emitted only `~/.cursor/skills/` for Cursor.

This PR wires a second artifact kind for `cursor` in
`runtime-artifact-layout.cts`: `convertedCommandsKind('commands', 'gsd-',
'convertClaudeCommandToCursorCommand', configDir)`. The new kind applies the
same `convertClaudeToCursorMarkdown` transforms (tool renames, brand
substitution, slash-command normalisation) and then strips YAML frontmatter
so the output is plain prose. Skills output is unchanged.

`stageCommandsForRuntimeFlat` in `install-profiles.cts` stages each source
`.md` as a flat `<stem>.md` in a temp dir; the existing `_copyStaged` commands
path then prefixes and copies to `<configDir>/commands/`.

`.cursor/mcp.json` is explicitly OUT OF SCOPE: GSD ships no MCP server; the
`mcpServers` schema cannot be usefully populated by the installer.

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

* refactor(#785): address review nit

---------

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

tests/install-runtime-artifacts.test.cjs

@@ -131,6 +131,31 @@ describe('installRuntimeArtifacts — gemini commands layout', () => {
   });
 });
 
+describe('installRuntimeArtifacts — cursor commands layout (#785)', () => {
+  test('cursor: skills/ AND commands/ both created; commands/gsd-help.md is plain markdown', (t) => {
+    const configDir = createTempDir('gsd-ial-cursor-cmds-');
+    t.after(() => cleanup(configDir));
+
+    installRuntimeArtifacts('cursor', configDir, 'global', RESOLVED_CORE);
+
+    // Existing skills kind still present
+    const skillsDir = path.join(configDir, 'skills');
+    assert.ok(fs.existsSync(skillsDir), 'skills/ must exist');
+    assert.ok(fs.existsSync(path.join(skillsDir, 'gsd-help', 'SKILL.md')),
+      'skills/gsd-help/SKILL.md must exist');
+
+    // New commands kind (#785)
+    const commandsDir = path.join(configDir, 'commands');
+    assert.ok(fs.existsSync(commandsDir), 'commands/ must exist (#785)');
+    assert.ok(fs.existsSync(path.join(commandsDir, 'gsd-help.md')),
+      'commands/gsd-help.md must exist (#785)');
+
+    // Cursor commands are plain markdown — no YAML frontmatter
+    const helpContent = fs.readFileSync(path.join(commandsDir, 'gsd-help.md'), 'utf8');
+    assert.ok(!helpContent.startsWith('---'), 'cursor commands must not start with YAML frontmatter');
+  });
+});
+
 describe('installRuntimeArtifacts — cline no-op', () => {
   test('cline: no kinds — call succeeds, no dirs created', (t) => {
     const configDir = createTempDir('gsd-ial-cline-');