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/types.ts

@@ -0,0 +1,36 @@
+/**
+ * roles/types.ts — Type definitions for the role registry.
+ *
+ * RoleConfig is the single interface describing everything about a role.
+ * All role-related behavior should be derived from this config.
+ */
+
+/** Configuration for a single worker role. */
+export type RoleConfig = {
+  /** Unique role identifier (e.g., "dev", "qa", "architect"). */
+  id: string;
+  /** Human-readable display name. */
+  displayName: string;
+  /** Valid levels for this role. */
+  levels: readonly string[];
+  /** Default level when none specified. */
+  defaultLevel: string;
+  /** Default model per level. */
+  models: Record<string, string>;
+  /** Emoji per level (used in announcements). */
+  emoji: Record<string, string>;
+  /** Fallback emoji when level-specific emoji not found. */
+  fallbackEmoji: string;
+  /** Valid completion results for this role. */
+  completionResults: readonly string[];
+  /** Regex pattern fragment for session key matching (e.g., "dev|qa|architect"). */
+  sessionKeyPattern: string;
+  /** Notification config per event type. */
+  notifications: {
+    onStart: boolean;
+    onComplete: boolean;
+  };
+};
+
+/** A role ID string (typed from registry keys). */
+export type RoleId = string;