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/SettingsModal.tsx

@@ -70,6 +70,18 @@ export function SettingsModal({ onClose }: SettingsModalProps) {
     }
   }
 
+  const handleTestingRatioChange = (ratio: number) => {
+    if (!updateSettings.isPending) {
+      updateSettings.mutate({ testing_agent_ratio: ratio })
+    }
+  }
+
+  const handleCountTestingToggle = () => {
+    if (settings && !updateSettings.isPending) {
+      updateSettings.mutate({ count_testing_in_concurrency: !settings.count_testing_in_concurrency })
+    }
+  }
+
   const models = modelsData?.models ?? []
   const isSaving = updateSettings.isPending
 
@@ -199,6 +211,76 @@ export function SettingsModal({ onClose }: SettingsModalProps) {
               </div>
             </div>
 
+            {/* Testing Agent Ratio */}
+            <div>
+              <label
+                id="testing-ratio-label"
+                className="font-display font-bold text-base block mb-1"
+              >
+                Testing Agents per Coding Agent
+              </label>
+              <p className="text-sm text-[var(--color-neo-text-secondary)] mb-2">
+                Regression testing agents spawned per coding agent (0 = disabled)
+              </p>
+              <div
+                className="flex border-3 border-[var(--color-neo-border)]"
+                role="radiogroup"
+                aria-labelledby="testing-ratio-label"
+              >
+                {[0, 1, 2, 3].map((ratio) => (
+                  <button
+                    key={ratio}
+                    onClick={() => handleTestingRatioChange(ratio)}
+                    disabled={isSaving}
+                    role="radio"
+                    aria-checked={settings.testing_agent_ratio === ratio}
+                    className={`flex-1 py-2 px-3 font-display font-bold text-sm transition-colors ${
+                      settings.testing_agent_ratio === ratio
+                        ? 'bg-[var(--color-neo-progress)] text-[var(--color-neo-text)]'
+                        : 'bg-[var(--color-neo-card)] text-[var(--color-neo-text)] hover:bg-[var(--color-neo-hover-subtle)]'
+                    } ${isSaving ? 'opacity-50 cursor-not-allowed' : ''}`}
+                  >
+                    {ratio}
+                  </button>
+                ))}
+              </div>
+            </div>
+
+            {/* Count Testing in Concurrency Toggle */}
+            <div>
+              <div className="flex items-center justify-between">
+                <div>
+                  <label
+                    id="count-testing-label"
+                    className="font-display font-bold text-base"
+                  >
+                    Count Testing in Concurrency
+                  </label>
+                  <p className="text-sm text-[var(--color-neo-text-secondary)] mt-1">
+                    If enabled, testing agents count toward the concurrency limit
+                  </p>
+                </div>
+                <button
+                  onClick={handleCountTestingToggle}
+                  disabled={isSaving}
+                  className={`relative w-14 h-8 rounded-none border-3 border-[var(--color-neo-border)] transition-colors ${
+                    settings.count_testing_in_concurrency
+                      ? 'bg-[var(--color-neo-progress)]'
+                      : 'bg-[var(--color-neo-card)]'
+                  } ${isSaving ? 'opacity-50 cursor-not-allowed' : ''}`}
+                  role="switch"
+                  aria-checked={settings.count_testing_in_concurrency}
+                  aria-labelledby="count-testing-label"
+                >
+                  <span
+                    className={`absolute top-1 w-5 h-5 bg-[var(--color-neo-border)] transition-transform ${
+                      settings.count_testing_in_concurrency ? 'left-7' : 'left-1'
+                    }`}
+                  />
+                </button>
+              </div>
+            </div>
+
             {/* Update Error */}
             {updateSettings.isError && (
               <div className="p-3 bg-[var(--color-neo-error-bg)] border-3 border-[var(--color-neo-error-border)] text-[var(--color-neo-error-text)] text-sm">