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

index.ts

@@ -10,6 +10,7 @@ import { createProjectRegisterTool } from "./lib/tools/project-register.js";
 import { createSetupTool } from "./lib/tools/setup.js";
 import { createOnboardTool } from "./lib/tools/onboard.js";
 import { createAutoConfigureModelsTool } from "./lib/tools/autoconfigure-models.js";
+import { createDesignTaskTool } from "./lib/tools/design-task.js";
 import { registerCli } from "./lib/cli.js";
 import { registerHeartbeatService } from "./lib/services/heartbeat.js";
 import { registerBootstrapHook } from "./lib/bootstrap-hook.js";
@@ -44,6 +45,14 @@ const plugin = {
               tester: { type: "string" },
             },
           },
+          architect: {
+            type: "object",
+            description: "Architect tier models",
+            properties: {
+              opus: { type: "string" },
+              sonnet: { type: "string" },
+            },
+          },
         },
       },
       projectExecution: {
@@ -99,6 +108,9 @@ const plugin = {
     api.registerTool(createTaskUpdateTool(api), { names: ["task_update"] });
     api.registerTool(createTaskCommentTool(api), { names: ["task_comment"] });
 
+    // Architect
+    api.registerTool(createDesignTaskTool(api), { names: ["design_task"] });
+
     // Operations
     api.registerTool(createStatusTool(api), { names: ["status"] });
     api.registerTool(createHealthTool(), { names: ["health"] });
@@ -124,7 +136,7 @@ const plugin = {
     registerBootstrapHook(api);
 
     api.logger.info(
-      "DevClaw plugin registered (11 tools, 1 CLI command group, 1 service, 1 hook)",
+      "DevClaw plugin registered (12 tools, 1 CLI command group, 1 service, 1 hook)",
     );
   },
 };