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/tools/health.ts

@@ -18,6 +18,7 @@ import { readProjects, getProject } from "../projects.js";
 import { log as auditLog } from "../audit.js";
 import { checkWorkerHealth, scanOrphanedLabels, fetchGatewaySessions, type HealthFix } from "../services/health.js";
 import { requireWorkspaceDir, resolveProvider } from "../tool-helpers.js";
+import { getAllRoleIds } from "../roles/index.js";
 
 export function createHealthTool() {
   return (ctx: ToolContext) => ({
@@ -51,13 +52,13 @@ export function createHealthTool() {
         if (!project) continue;
         const { provider } = await resolveProvider(project);
 
-        for (const role of ["dev", "qa", "architect"] as const) {
+        for (const role of getAllRoleIds()) {
           // Worker health check (session liveness, label consistency, etc)
           const healthFixes = await checkWorkerHealth({
             workspaceDir,
             groupId: pid,
             project,
-            role,
+            role: role as any,
             sessions,
             autoFix: fix,
             provider,
@@ -69,7 +70,7 @@ export function createHealthTool() {
             workspaceDir,
             groupId: pid,
             project,
-            role,
+            role: role as any,
             autoFix: fix,
             provider,
           });