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/index.ts

@@ -11,7 +11,7 @@ export {
 	type PromptOptions,
 	type SessionStats,
 } from "./agent-session.js";
-export { type BashExecutorOptions, type BashResult, executeBash } from "./bash-executor.js";
+export { type BashExecutorOptions, type BashResult, executeBash, executeBashWithOperations } from "./bash-executor.js";
 export type { CompactionResult } from "./compaction/index.js";
 export { createEventBus, type EventBus, type EventBusController } from "./event-bus.js";