refactor: migrate role handling from tiers to roles module

- Removed the deprecated tiers.ts file and migrated all related functionality to roles/index.js.
- Updated tests and tools to reflect the new role structure, replacing references to "dev", "qa", and "architect" with "developer", "tester", and "architect".
- Adjusted workflow configurations and state management to accommodate the new role naming conventions.
- Enhanced project registration and health check tools to support dynamic role handling.
- Updated task creation, update, and completion processes to align with the new role definitions.
- Improved documentation and comments to clarify role responsibilities and usage.

lib/config/index.ts

@@ -0,0 +1,14 @@
+/**
+ * config/ — Unified DevClaw configuration.
+ *
+ * Single config.yaml per workspace/project combining roles, models, and workflow.
+ */
+export type {
+  DevClawConfig,
+  RoleOverride,
+  ResolvedConfig,
+  ResolvedRoleConfig,
+} from "./types.js";
+
+export { loadConfig } from "./loader.js";
+export { mergeConfig } from "./merge.js";