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/tools/project-register.ts

@@ -14,8 +14,8 @@ import { readProjects, writeProjects, emptyWorkerState } from "../projects.js";
 import { resolveRepoPath } from "../projects.js";
 import { createProvider } from "../providers/index.js";
 import { log as auditLog } from "../audit.js";
-import { DEV_LEVELS, QA_LEVELS } from "../tiers.js";
-import { DEFAULT_DEV_INSTRUCTIONS, DEFAULT_QA_INSTRUCTIONS } from "../templates.js";
+import { DEV_LEVELS, QA_LEVELS, ARCHITECT_LEVELS } from "../tiers.js";
+import { DEFAULT_DEV_INSTRUCTIONS, DEFAULT_QA_INSTRUCTIONS, DEFAULT_ARCHITECT_INSTRUCTIONS } from "../templates.js";
 
 /**
  * Scaffold project-specific prompt files.
@@ -43,6 +43,14 @@ async function scaffoldPromptFiles(workspaceDir: string, projectName: string): P
     created = true;
   }
 
+  const projectArchitect = path.join(projectDir, "architect.md");
+  try {
+    await fs.access(projectArchitect);
+  } catch {
+    await fs.writeFile(projectArchitect, DEFAULT_ARCHITECT_INSTRUCTIONS, "utf-8");
+    created = true;
+  }
+
   return created;
 }
 
@@ -141,7 +149,7 @@ export function createProjectRegisterTool() {
         );
       }
 
-      // 4. Create all 8 state labels (idempotent)
+      // 4. Create all state labels (idempotent)
       await provider.ensureAllStateLabels();
 
       // 5. Add project to projects.json
@@ -156,6 +164,7 @@ export function createProjectRegisterTool() {
         roleExecution,
         dev: emptyWorkerState([...DEV_LEVELS]),
         qa: emptyWorkerState([...QA_LEVELS]),
+        architect: emptyWorkerState([...ARCHITECT_LEVELS]),
       };
 
       await writeProjects(workspaceDir, data);
@@ -184,7 +193,7 @@ export function createProjectRegisterTool() {
         repo,
         baseBranch,
         deployBranch,
-        labelsCreated: 8,
+        labelsCreated: 10,
         promptsScaffolded: promptsCreated,
         announcement,
       });