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/workflow.ts

@@ -17,7 +17,7 @@ import path from "node:path";
 // ---------------------------------------------------------------------------
 
 export type StateType = "queue" | "active" | "hold" | "terminal";
-export type Role = "dev" | "qa";
+export type Role = "dev" | "qa" | "architect";
 export type TransitionAction = "gitPull" | "detectPr" | "closeIssue" | "reopenIssue";
 
 export type TransitionTarget = string | {
@@ -118,6 +118,24 @@ export const DEFAULT_WORKFLOW: WorkflowConfig = {
       label: "Done",
       color: "#5cb85c",
     },
+    toDesign: {
+      type: "queue",
+      role: "architect",
+      label: "To Design",
+      color: "#0075ca",
+      priority: 1,
+      on: { PICKUP: "designing" },
+    },
+    designing: {
+      type: "active",
+      role: "architect",
+      label: "Designing",
+      color: "#d4c5f9",
+      on: {
+        COMPLETE: "planning",
+        BLOCKED: "refining",
+      },
+    },
   },
 };
 
@@ -295,6 +313,8 @@ const RESULT_TO_EVENT: Record<string, string> = {
   "qa:fail": "FAIL",
   "qa:refine": "REFINE",
   "qa:blocked": "BLOCKED",
+  "architect:done": "COMPLETE",
+  "architect:blocked": "BLOCKED",
 };
 
 /**
@@ -369,6 +389,8 @@ export function getCompletionEmoji(role: Role, result: string): string {
     "qa:refine": "🤔",
     "dev:blocked": "🚫",
     "qa:blocked": "🚫",
+    "architect:done": "🏗️",
+    "architect:blocked": "🚫",
   };
   return map[`${role}:${result}`] ?? "📋";
 }