feat(quality-rails): migrate @mosaic/quality-rails from v0 to v1

Implements the full quality-rails scaffolding package in v1:
- types.ts: ProjectKind, QualityProfile, RailsConfig, ScaffoldResult
- detect.ts: project kind detection (node/python/rust/unknown)
- templates.ts: ESLint, Biome, pyproject, rustfmt, pre-commit, PR checklist templates
- scaffolder.ts: core scaffolding engine with file writing and dependency installation
- cli.ts: Commander.js CLI with init/check/doctor subcommands
- index.ts: re-exports all public API
- package.json: adds commander dep, type=module, @types/node devDep

All three quality gates pass (format:check, typecheck, lint).

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

packages/quality-rails/src/detect.ts

@@ -0,0 +1,30 @@
+import { constants } from 'node:fs';
+import { access } from 'node:fs/promises';
+import { join } from 'node:path';
+
+import type { ProjectKind } from './types.js';
+
+async function fileExists(filePath: string): Promise<boolean> {
+  try {
+    await access(filePath, constants.F_OK);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export async function detectProjectKind(projectPath: string): Promise<ProjectKind> {
+  if (await fileExists(join(projectPath, 'package.json'))) {
+    return 'node';
+  }
+
+  if (await fileExists(join(projectPath, 'pyproject.toml'))) {
+    return 'python';
+  }
+
+  if (await fileExists(join(projectPath, 'Cargo.toml'))) {
+    return 'rust';
+  }
+
+  return 'unknown';
+}