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>

src/shared/contracts/ipc.ts

@@ -1,5 +1,5 @@
 import type { ApprovalDecision } from '@shared/domain/approval';
-import type { SidecarCapabilities, InteractionMode } from '@shared/contracts/sidecar';
+import type { SidecarCapabilities, InteractionMode, MessageMode } from '@shared/contracts/sidecar';
 import type { PatternDefinition, ReasoningEffort } from '@shared/domain/pattern';
 import type { ProjectRecord } from '@shared/domain/project';
 import type { QuerySessionsInput, SessionQueryResult } from '@shared/domain/sessionLibrary';
@@ -11,6 +11,7 @@ import type {
   AppearanceTheme,
 } from '@shared/domain/tooling';
 import type { WorkspaceState } from '@shared/domain/workspace';
+import type { ChatMessageAttachment } from '@shared/domain/attachment';
 
 export interface CreateSessionInput {
   projectId: string;
@@ -24,6 +25,8 @@ export interface SavePatternInput {
 export interface SendSessionMessageInput {
   sessionId: string;
   content: string;
+  attachments?: ChatMessageAttachment[];
+  messageMode?: MessageMode;
 }
 
 export interface CancelSessionTurnInput {
@@ -125,6 +128,10 @@ export interface StartSessionMcpAuthInput {
   sessionId: string;
 }
 
+export interface DeleteSessionInput {
+  sessionId: string;
+}
+
 export interface ElectronApi {
   describeSidecarCapabilities(): Promise<SidecarCapabilities>;
   refreshSidecarCapabilities(): Promise<SidecarCapabilities>;
@@ -148,6 +155,7 @@ export interface ElectronApi {
   renameSession(input: RenameSessionInput): Promise<WorkspaceState>;
   setSessionPinned(input: SetSessionPinnedInput): Promise<WorkspaceState>;
   setSessionArchived(input: SetSessionArchivedInput): Promise<WorkspaceState>;
+  deleteSession(input: DeleteSessionInput): Promise<WorkspaceState>;
   sendSessionMessage(input: SendSessionMessageInput): Promise<void>;
   cancelSessionTurn(input: CancelSessionTurnInput): Promise<void>;
   resolveSessionApproval(input: ResolveSessionApprovalInput): Promise<WorkspaceState>;