feat: add dedicated testing agents and enhanced parallel orchestration

Introduce a new testing agent architecture that runs regression tests
independently from coding agents, improving quality assurance in
parallel mode.

Key changes:

Testing Agent System:
- Add testing_prompt.template.md for dedicated testing agent role
- Add feature_mark_failing MCP tool for regression detection
- Add --agent-type flag to select initializer/coding/testing mode
- Remove regression testing from coding prompt (now handled by testing agents)

Parallel Orchestrator Enhancements:
- Add testing agent spawning with configurable ratio (--testing-agent-ratio)
- Add comprehensive debug logging system (DebugLog class)
- Improve database session management to prevent stale reads
- Add engine.dispose() calls to refresh connections after subprocess commits
- Fix f-string linting issues (remove unnecessary f-prefixes)

UI Improvements:
- Add testing agent mascot (Chip) to AgentAvatar
- Enhance AgentCard to display testing agent status
- Add testing agent ratio slider in SettingsModal
- Update WebSocket handling for testing agent updates
- Improve ActivityFeed to show testing agent activity

API & Server Updates:
- Add testing_agent_ratio to settings schema and endpoints
- Update process manager to support testing agent type
- Enhance WebSocket messages for agent_update events

Template Changes:
- Delete coding_prompt_yolo.template.md (consolidated into main prompt)
- Update initializer_prompt.template.md with improved structure
- Streamline coding_prompt.template.md workflow

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ui/src/components/SpecCreationChat.tsx

@@ -6,7 +6,7 @@
  */
 
 import { useCallback, useEffect, useRef, useState } from 'react'
-import { Send, X, CheckCircle2, AlertCircle, Wifi, WifiOff, RotateCcw, Loader2, ArrowRight, Zap, Paperclip, ExternalLink } from 'lucide-react'
+import { Send, X, CheckCircle2, AlertCircle, Wifi, WifiOff, RotateCcw, Loader2, ArrowRight, Zap, Paperclip, ExternalLink, FileText } from 'lucide-react'
 import { useSpecChat } from '../hooks/useSpecChat'
 import { ChatMessage } from './ChatMessage'
 import { QuestionOptions } from './QuestionOptions'
@@ -17,6 +17,24 @@ import type { ImageAttachment } from '../lib/types'
 const MAX_FILE_SIZE = 5 * 1024 * 1024 // 5 MB
 const ALLOWED_TYPES = ['image/jpeg', 'image/png']
 
+// Sample prompt for quick testing
+const SAMPLE_PROMPT = `Let's call it Simple Todo. This is a really simple web app that I can use to track my to-do items using a Kanban board. I should be able to add to-dos and then drag and drop them through the Kanban board. The different columns in the Kanban board are:
+
+- To Do
+- In Progress
+- Done
+
+The app should use a neobrutalism design.
+
+There is no need for user authentication either. All the to-dos will be stored in local storage, so each user has access to all of their to-dos when they open their browser. So do not worry about implementing a backend with user authentication or a database. Simply store everything in local storage. As for the design, please try to avoid AI slop, so use your front-end design skills to design something beautiful and practical. As for the content of the to-dos, we should store:
+
+- The name or the title at the very least
+- Optionally, we can also set tags, due dates, and priorities which should be represented as beautiful little badges on the to-do card
+
+Users should have the ability to easily clear out all the completed To-Dos. They should also be able to filter and search for To-Dos as well.
+
+You choose the rest. Keep it simple. Should be 25 features.`
+
 type InitializerStatus = 'idle' | 'starting' | 'error'
 
 interface SpecCreationChatProps {
@@ -223,6 +241,23 @@ export function SpecCreationChat({
             </span>
           )}
 
+          {/* Load Sample Prompt */}
+          <button
+            onClick={() => {
+              setInput(SAMPLE_PROMPT)
+              // Also resize the textarea to fit content
+              if (inputRef.current) {
+                inputRef.current.style.height = 'auto'
+                inputRef.current.style.height = `${Math.min(inputRef.current.scrollHeight, 200)}px`
+              }
+            }}
+            className="neo-btn neo-btn-ghost text-sm py-2"
+            title="Load sample prompt (Simple Todo app)"
+          >
+            <FileText size={16} />
+            Load Sample
+          </button>
+
           {/* Exit to Project - always visible escape hatch */}
           <button
             onClick={onExitToProject}