feat(coding-agent): add user_bash event and theme API extensions

- user_bash event for intercepting ! and !! commands (#528)
- Extensions can return { operations } or { result } to redirect/replace
- executeBashWithOperations() for custom BashOperations execution
- session.recordBashResult() for extensions handling bash themselves
- Theme API: getAllThemes(), getTheme(), setTheme() on ctx.ui
- mac-system-theme.ts example: sync with macOS dark/light mode
- Updated ssh.ts to use user_bash event

packages/coding-agent/src/core/extensions/index.ts

@@ -103,6 +103,9 @@ export type {
 	TreePreparation,
 	TurnEndEvent,
 	TurnStartEvent,
+	// Events - User Bash
+	UserBashEvent,
+	UserBashEventResult,
 	WriteToolResultEvent,
 } from "./types.js";
 // Type guards