feat: add concurrent agents with dependency system and delightful UI

Major feature implementation for parallel agent execution with dependency-aware
scheduling and an engaging multi-agent UI experience.

Backend Changes:
- Add parallel_orchestrator.py for concurrent feature processing
- Add api/dependency_resolver.py with cycle detection (Kahn's algorithm + DFS)
- Add atomic feature_claim_next() with retry limit and exponential backoff
- Fix circular dependency check arguments in 4 locations
- Add AgentTracker class for parsing agent output and emitting updates
- Add browser isolation with --isolated flag for Playwright MCP
- Extend WebSocket protocol with agent_update messages and log attribution
- Add WSAgentUpdateMessage schema with agent states and mascot names
- Fix WSProgressMessage to include in_progress field

New UI Components:
- AgentMissionControl: Dashboard showing active agents with collapsible activity
- AgentCard: Individual agent status with avatar and thought bubble
- AgentAvatar: SVG mascots (Spark, Fizz, Octo, Hoot, Buzz) with animations
- ActivityFeed: Recent activity stream with stable keys (no flickering)
- CelebrationOverlay: Confetti animation with click/Escape dismiss
- DependencyGraph: Interactive node graph visualization with dagre layout
- DependencyBadge: Visual indicator for feature dependencies
- ViewToggle: Switch between Kanban and Graph views
- KeyboardShortcutsHelp: Help overlay accessible via ? key

UI/UX Improvements:
- Celebration queue system to handle rapid success messages
- Accessibility attributes on AgentAvatar (role, aria-label, aria-live)
- Collapsible Recent Activity section with persisted preference
- Agent count display in header
- Keyboard shortcut G to toggle Kanban/Graph view
- Real-time thought bubbles and state animations

Bug Fixes:
- Fix circular dependency validation (swapped source/target arguments)
- Add MAX_CLAIM_RETRIES=10 to prevent stack overflow under contention
- Fix THOUGHT_PATTERNS to match actual [Tool: name] format
- Fix ActivityFeed key prop to prevent re-renders on new items
- Add featureId/agentIndex to log messages for proper attribution

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

ui/src/components/DependencyBadge.tsx

@@ -0,0 +1,121 @@
+import { AlertTriangle, GitBranch, Check } from 'lucide-react'
+import type { Feature } from '../lib/types'
+
+interface DependencyBadgeProps {
+  feature: Feature
+  allFeatures?: Feature[]
+  compact?: boolean
+}
+
+/**
+ * Badge component showing dependency status for a feature.
+ * Shows:
+ * - Blocked status with count of blocking dependencies
+ * - Dependency count for features with satisfied dependencies
+ * - Nothing if feature has no dependencies
+ */
+export function DependencyBadge({ feature, allFeatures = [], compact = false }: DependencyBadgeProps) {
+  const dependencies = feature.dependencies || []
+
+  if (dependencies.length === 0) {
+    return null
+  }
+
+  // Use API-computed blocked status if available, otherwise compute locally
+  const isBlocked = feature.blocked ??
+    (feature.blocking_dependencies && feature.blocking_dependencies.length > 0) ??
+    false
+
+  const blockingCount = feature.blocking_dependencies?.length ?? 0
+
+  // Compute satisfied count from allFeatures if available
+  let satisfiedCount = dependencies.length - blockingCount
+  if (allFeatures.length > 0 && !feature.blocking_dependencies) {
+    const passingIds = new Set(allFeatures.filter(f => f.passes).map(f => f.id))
+    satisfiedCount = dependencies.filter(d => passingIds.has(d)).length
+  }
+
+  if (compact) {
+    // Compact view for card displays
+    return (
+      <div
+        className={`
+          inline-flex items-center gap-1 text-xs px-2 py-0.5 rounded-full font-mono
+          ${isBlocked
+            ? 'bg-neo-danger/20 text-neo-danger'
+            : 'bg-neo-neutral-200 text-neo-text-secondary'
+          }
+        `}
+        title={isBlocked
+          ? `Blocked by ${blockingCount} ${blockingCount === 1 ? 'dependency' : 'dependencies'}`
+          : `${satisfiedCount}/${dependencies.length} dependencies satisfied`
+        }
+      >
+        {isBlocked ? (
+          <>
+            <AlertTriangle size={12} />
+            <span>{blockingCount}</span>
+          </>
+        ) : (
+          <>
+            <GitBranch size={12} />
+            <span>{satisfiedCount}/{dependencies.length}</span>
+          </>
+        )}
+      </div>
+    )
+  }
+
+  // Full view with more details
+  return (
+    <div className="flex items-center gap-2">
+      {isBlocked ? (
+        <div className="flex items-center gap-1.5 text-sm text-neo-danger">
+          <AlertTriangle size={14} />
+          <span className="font-medium">
+            Blocked by {blockingCount} {blockingCount === 1 ? 'dependency' : 'dependencies'}
+          </span>
+        </div>
+      ) : (
+        <div className="flex items-center gap-1.5 text-sm text-neo-text-secondary">
+          <Check size={14} className="text-neo-done" />
+          <span>
+            All {dependencies.length} {dependencies.length === 1 ? 'dependency' : 'dependencies'} satisfied
+          </span>
+        </div>
+      )}
+    </div>
+  )
+}
+
+/**
+ * Small inline indicator for dependency status
+ */
+export function DependencyIndicator({ feature }: { feature: Feature }) {
+  const dependencies = feature.dependencies || []
+  const isBlocked = feature.blocked || (feature.blocking_dependencies && feature.blocking_dependencies.length > 0)
+
+  if (dependencies.length === 0) {
+    return null
+  }
+
+  if (isBlocked) {
+    return (
+      <span
+        className="inline-flex items-center justify-center w-5 h-5 rounded-full bg-neo-danger/20 text-neo-danger"
+        title={`Blocked by ${feature.blocking_dependencies?.length || 0} dependencies`}
+      >
+        <AlertTriangle size={12} />
+      </span>
+    )
+  }
+
+  return (
+    <span
+      className="inline-flex items-center justify-center w-5 h-5 rounded-full bg-neo-neutral-200 text-neo-text-secondary"
+      title={`${dependencies.length} dependencies (all satisfied)`}
+    >
+      <GitBranch size={12} />
+    </span>
+  )
+}