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/services/pipeline.ts

@@ -26,24 +26,28 @@ import {
  * Kept for backward compatibility.
  */
 export const COMPLETION_RULES: Record<string, CompletionRule> = {
-  "dev:done":    { from: "Doing",   to: "To Test",    gitPull: true, detectPr: true },
-  "qa:pass":     { from: "Testing", to: "Done",       closeIssue: true },
-  "qa:fail":     { from: "Testing", to: "To Improve", reopenIssue: true },
-  "qa:refine":   { from: "Testing", to: "Refining" },
-  "dev:blocked": { from: "Doing",   to: "Refining" },
-  "qa:blocked":  { from: "Testing", to: "Refining" },
+  "dev:done":       { from: "Doing",     to: "To Test",    gitPull: true, detectPr: true },
+  "qa:pass":        { from: "Testing",   to: "Done",       closeIssue: true },
+  "qa:fail":        { from: "Testing",   to: "To Improve", reopenIssue: true },
+  "qa:refine":      { from: "Testing",   to: "Refining" },
+  "dev:blocked":    { from: "Doing",     to: "Refining" },
+  "qa:blocked":     { from: "Testing",   to: "Refining" },
+  "architect:done": { from: "Designing", to: "Planning" },
+  "architect:blocked": { from: "Designing", to: "Refining" },
 };
 
 /**
  * @deprecated Use getNextStateDescription() from workflow.ts instead.
  */
 export const NEXT_STATE: Record<string, string> = {
-  "dev:done":    "QA queue",
-  "dev:blocked": "moved to Refining - needs human input",
-  "qa:pass":     "Done!",
-  "qa:fail":     "back to DEV",
-  "qa:refine":   "awaiting human decision",
-  "qa:blocked":  "moved to Refining - needs human input",
+  "dev:done":         "QA queue",
+  "dev:blocked":      "moved to Refining - needs human input",
+  "qa:pass":          "Done!",
+  "qa:fail":          "back to DEV",
+  "qa:refine":        "awaiting human decision",
+  "qa:blocked":       "moved to Refining - needs human input",
+  "architect:done":   "Planning — ready for review",
+  "architect:blocked": "moved to Refining - needs clarification",
 };
 
 // Re-export CompletionRule type for backward compatibility
@@ -77,7 +81,7 @@ export function getRule(
 export async function executeCompletion(opts: {
   workspaceDir: string;
   groupId: string;
-  role: "dev" | "qa";
+  role: "dev" | "qa" | "architect";
   result: string;
   issueId: number;
   summary?: string;