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/services/heartbeat.ts

@@ -18,6 +18,7 @@ import { log as auditLog } from "../audit.js";
 import { checkWorkerHealth, scanOrphanedLabels, fetchGatewaySessions, type SessionLookup } from "./health.js";
 import { projectTick } from "./tick.js";
 import { createProvider } from "../providers/index.js";
+import { getAllRoleIds } from "../roles/index.js";
 
 // ---------------------------------------------------------------------------
 // Types
@@ -306,13 +307,13 @@ async function performHealthPass(
   const { provider } = await createProvider({ repo: project.repo });
   let fixedCount = 0;
 
-  for (const role of ["dev", "qa", "architect"] as const) {
+  for (const role of getAllRoleIds()) {
     // Check worker health (session liveness, label consistency, etc)
     const healthFixes = await checkWorkerHealth({
       workspaceDir,
       groupId,
       project,
-      role,
+      role: role as any,
       sessions,
       autoFix: true,
       provider,
@@ -324,7 +325,7 @@ async function performHealthPass(
       workspaceDir,
       groupId,
       project,
-      role,
+      role: role as any,
       autoFix: true,
       provider,
     });