feat(tui): diff viewer, workflow picker, cursor support, and approval reconnect fix

- Add unified diff viewer for file_write/file_edit tools across all layers:
  ToolReceipt.diff → DiffUtil (LCS-based) → SandboxedToolExecutor → ToolCompleted
  → TuiToolRecord.diff → DiffViewer widget (colored +/- lines)
- Add workflow selection panel: WorkflowList server message, WorkflowListPanel
  widget, ↑↓ seamlessly extends into workflow picker from session list
- Add cursor/caret support: inputCursor in TuiState, CursorLeft/CursorRight
  actions and key events, AppendChar inserts at cursor, Backspace deletes before
- Colorize event history strip (green/red/yellow/blue by type) and input bar
  (blue/yellow prompt, cyan session name, blue keybindings)
- Show 5 recent events instead of 3; increase event strip height to 6
- Remove lastEventAt sort so display and navigation use consistent order
- Fix approval reconnect: register pending approvals with ApprovalCoordinator
  during snapshot replay so lookupSession works after reconnect
- 167 tests pass (126 TUI + 41 server)

core/events/src/main/kotlin/com/correx/core/events/events/ToolReceipt.kt

@@ -17,5 +17,6 @@ data class ToolReceipt(
     val affectedEntities: List<String> = emptyList(),
     val durationMs: Long,
     val tier: Tier,
-    val timestamp: Instant
+    val timestamp: Instant,
+    val diff: String? = null,
 )