refactor: Centralize role types and configuration (#190)

Creates a single source of truth for all worker roles via lib/roles/.

## New: lib/roles/

- **registry.ts** — All role definitions (dev, qa, architect) with
  levels, models, emoji, completion results, session key patterns
- **types.ts** — RoleConfig interface
- **selectors.ts** — Query helpers: getRole(), getLevelsForRole(),
  resolveModel(), isValidResult(), roleForLevel(), etc.
- **index.ts** — Barrel exports

## Migrated Files

- **lib/tiers.ts** — Now delegates to registry (backward compat kept)
- **lib/dispatch.ts** — Uses registry for emoji resolution
- **lib/bootstrap-hook.ts** — Uses registry for session key pattern
- **lib/services/tick.ts** — Uses registry for level detection
- **lib/services/heartbeat.ts** — Uses registry for role iteration
- **lib/tools/health.ts** — Uses registry for role iteration
- **lib/tools/work-start.ts** — Uses registry for role enum
- **lib/tools/work-finish.ts** — Uses registry for result validation
- **lib/tools/project-register.ts** — Uses registry for level lists

## Key Benefits

- Adding a new role = add entry to registry.ts (single file)
- No more scattered role unions ("dev" | "qa" | "architect")
- Type-safe role/level/result validation from registry
- Session key pattern auto-generated from registry
- All 64 tests passing (22 new registry tests + 42 existing)

lib/roles/index.ts

@@ -0,0 +1,36 @@
+/**
+ * roles/ — Centralized role configuration.
+ *
+ * Single source of truth for all worker roles in DevClaw.
+ * To add a new role, add an entry to registry.ts — everything else derives from it.
+ */
+export { ROLE_REGISTRY } from "./registry.js";
+export type { RoleConfig, RoleId } from "./types.js";
+export {
+  // Role IDs
+  type WorkerRole,
+  getAllRoleIds,
+  isValidRole,
+  getRole,
+  requireRole,
+  // Levels
+  getLevelsForRole,
+  getAllLevels,
+  isLevelForRole,
+  roleForLevel,
+  getDefaultLevel,
+  // Models
+  getDefaultModel,
+  getAllDefaultModels,
+  resolveModel,
+  // Emoji
+  getEmoji,
+  getFallbackEmoji,
+  // Completion
+  getCompletionResults,
+  isValidResult,
+  // Session keys
+  getSessionKeyRolePattern,
+  // Notifications
+  isNotificationEnabled,
+} from "./selectors.js";