feat: Implement Architect role & design_task tool (#189)

Adds the Architect role for design/architecture investigations with
persistent sessions and structured design proposals.

## New Features

- **Architect role** with opus (complex) and sonnet (standard) levels
- **design_task tool** — Creates To Design issues and dispatches architect
- **Workflow states:** To Design → Designing → Planning
- **Completion rules:** architect:done → Planning, architect:blocked → Refining
- **Auto-level selection** based on complexity keywords

## Files Changed (22 files, 546 additions)

### New Files
- lib/tools/design-task.ts — design_task tool implementation
- lib/tools/design-task.test.ts — 16 tests for architect functionality

### Core Changes
- lib/tiers.ts — ARCHITECT_LEVELS, WorkerRole type, models, emoji
- lib/workflow.ts — toDesign/designing states, completion rules
- lib/projects.ts — architect WorkerState on Project type
- lib/dispatch.ts — architect role support in dispatch pipeline
- lib/services/pipeline.ts — architect completion rules
- lib/model-selector.ts — architect level selection heuristic

### Integration
- index.ts — Register design_task tool, architect config schema
- lib/notify.ts — architect role in notifications
- lib/bootstrap-hook.ts — architect session key parsing
- lib/services/tick.ts — architect in queue processing
- lib/services/heartbeat.ts — architect in health checks
- lib/tools/health.ts — architect in health scans
- lib/tools/status.ts — architect in status dashboard
- lib/tools/work-start.ts — architect role option
- lib/tools/work-finish.ts — architect validation
- lib/tools/project-register.ts — architect labels + role scaffolding
- lib/templates.ts — architect instructions + AGENTS.md updates
- lib/setup/workspace.ts — architect role file scaffolding
- lib/setup/smart-model-selector.ts — architect in model assignment
- lib/setup/llm-model-selector.ts — architect in LLM prompt

lib/projects.ts

@@ -28,6 +28,7 @@ export type Project = {
   maxQaWorkers?: number;
   dev: WorkerState;
   qa: WorkerState;
+  architect: WorkerState;
 };
 
 export type ProjectsData = {
@@ -86,6 +87,9 @@ export async function readProjects(workspaceDir: string): Promise<ProjectsData>
     project.qa = project.qa
       ? parseWorkerState(project.qa as unknown as Record<string, unknown>)
       : emptyWorkerState([]);
+    project.architect = project.architect
+      ? parseWorkerState(project.architect as unknown as Record<string, unknown>)
+      : emptyWorkerState([]);
     if (!project.channel) {
       project.channel = "telegram";
     }
@@ -113,7 +117,7 @@ export function getProject(
 
 export function getWorker(
   project: Project,
-  role: "dev" | "qa",
+  role: "dev" | "qa" | "architect",
 ): WorkerState {
   return project[role];
 }
@@ -125,7 +129,7 @@ export function getWorker(
 export async function updateWorker(
   workspaceDir: string,
   groupId: string,
-  role: "dev" | "qa",
+  role: "dev" | "qa" | "architect",
   updates: Partial<WorkerState>,
 ): Promise<ProjectsData> {
   const data = await readProjects(workspaceDir);
@@ -153,7 +157,7 @@ export async function updateWorker(
 export async function activateWorker(
   workspaceDir: string,
   groupId: string,
-  role: "dev" | "qa",
+  role: "dev" | "qa" | "architect",
   params: {
     issueId: string;
     level: string;
@@ -183,7 +187,7 @@ export async function activateWorker(
 export async function deactivateWorker(
   workspaceDir: string,
   groupId: string,
-  role: "dev" | "qa",
+  role: "dev" | "qa" | "architect",
 ): Promise<ProjectsData> {
   return updateWorker(workspaceDir, groupId, role, {
     active: false,