feat: full Copilot SDK feature parity — custom agents, hooks, image input, skills, steering, session persistence

Backend (sidecar):
- Extended ProtocolModels with DTOs for custom agents, hooks, skills,
  infinite sessions, session lifecycle, and 9 new event types
- Added CopilotManagedSessionIds for stable SDK session ID mapping
- Added CopilotSessionManager/ICopilotSessionManager for session lifecycle
- Added CopilotSessionHooks for hook registration
- Added CopilotMessageOptionsMetadata for mid-turn steering
- Extended CopilotAgentBundle to wire custom agents, hooks, skills,
  infinite sessions, and stable session IDs
- Extended CopilotTurnExecutionState to project 13 new SDK event types
- Widened ITurnWorkflowRunner callback to accept SidecarEventDto
- Added list/delete/disconnect session commands to SidecarProtocolHost
- Added AryxCopilotAgentMessageOptionsTests (14 new tests, 142 total)

Frontend (renderer + main + shared):
- Added ChatMessageAttachment type and helpers (attachment.ts)
- Extended sidecar contracts with MessageMode, 3 new command types,
  9 new event types, and agent/session config DTOs
- Extended SessionEventRecord with 6 new event kinds and ~20 fields
- Added PatternAgentCopilotConfig to pattern domain
- Added attachments support to ChatMessageRecord
- Updated sidecar client with session lifecycle methods and
  turn-scoped event routing via onTurnScopedEvent callback
- Updated main process: handleTurnScopedEvent(), deleteSession(),
  steering bypass for mid-turn messages, attachment passthrough
- Added deleteSession IPC handler and preload binding
- Added TurnEventLog state tracker with format/apply/prune helpers
- ChatPane: always-enabled composer, steering indicator, attachment
  picker with preview, image thumbnails in message history,
  context-usage bar, amber steer mode for send button
- ActivityPanel: turn events section with sub-agent, hook, skill,
  and compaction event rendering
- Sidebar: delete session action in context menu
- App.tsx: wired sessionUsage, turnEventLogs, and deleteSession

Documentation:
- AGENTS.md: added glob safety rule for node_modules
- README.md: added steering, image input, and richer observability
- ARCHITECTURE.md: added turn-scoped events, steering, and attachments
- Website: added steering and image input feature cards, updated
  live visibility and session cards

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/src/pages/index.astro

@@ -141,7 +141,7 @@ import Base from '../layouts/Base.astro';
           </div>
           <h3 class="text-base font-semibold">Live Visibility</h3>
           <p class="mt-2 text-sm leading-relaxed text-zinc-400">
-            Watch each agent think, use tools, and hand off work in real time. Know exactly what's happening during complex runs.
+            Watch each agent think, delegate to sub-agents, invoke skills, and run hooks in real time. A context-usage bar shows how much of the model's window you've used.
           </p>
         </div>
 
@@ -154,11 +154,37 @@ import Base from '../layouts/Base.astro';
           </div>
           <h3 class="text-base font-semibold">Persistent Sessions</h3>
           <p class="mt-2 text-sm leading-relaxed text-zinc-400">
-            Rename, pin, archive, and return to sessions later. Your work persists instead of disappearing after each conversation.
+            Rename, pin, archive, delete, and return to sessions later. Your work persists instead of disappearing after each conversation.
           </p>
         </div>
 
-        <!-- Feature 6: Model Selection -->
+        <!-- Feature 6: Mid-turn Steering -->
+        <div class="group rounded-2xl border border-zinc-800 bg-zinc-900/40 p-6 transition hover:border-zinc-700 hover:bg-zinc-900/60">
+          <div class="mb-4 flex size-10 items-center justify-center rounded-xl bg-yellow-500/10 text-yellow-400">
+            <svg class="size-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M13 10V3L4 14h7v7l9-11h-7z" />
+            </svg>
+          </div>
+          <h3 class="text-base font-semibold">Steer While It Works</h3>
+          <p class="mt-2 text-sm leading-relaxed text-zinc-400">
+            Send follow-up messages while an agent is running. Your input is injected immediately so you can redirect without waiting.
+          </p>
+        </div>
+
+        <!-- Feature 7: Image Attachments -->
+        <div class="group rounded-2xl border border-zinc-800 bg-zinc-900/40 p-6 transition hover:border-zinc-700 hover:bg-zinc-900/60">
+          <div class="mb-4 flex size-10 items-center justify-center rounded-xl bg-pink-500/10 text-pink-400">
+            <svg class="size-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 16l4.586-4.586a2 2 0 012.828 0L16 16m-2-2l1.586-1.586a2 2 0 012.828 0L20 14m-6-6h.01M6 20h12a2 2 0 002-2V6a2 2 0 00-2-2H6a2 2 0 00-2 2v12a2 2 0 002 2z" />
+            </svg>
+          </div>
+          <h3 class="text-base font-semibold">Image Input</h3>
+          <p class="mt-2 text-sm leading-relaxed text-zinc-400">
+            Attach screenshots, diagrams, or photos to any message. The model sees the image alongside your text for visual reasoning.
+          </p>
+        </div>
+
+        <!-- Feature 8: Model Selection -->
         <div class="group rounded-2xl border border-zinc-800 bg-zinc-900/40 p-6 transition hover:border-zinc-700 hover:bg-zinc-900/60">
           <div class="mb-4 flex size-10 items-center justify-center rounded-xl bg-rose-500/10 text-rose-400">
             <svg class="size-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">