feat: add prepush lifecycle hook (#498)

* feat: add prepush lifecycle hook

Add `prepushScript` configuration — an optional shell script that runs
automatically before pushing code to the remote repository. Reuses the
existing `executeLifecycleHook` infrastructure (bash execution, 2-min
timeout, error propagation on non-zero exit). When unconfigured the
hook is a no-op.

Made-with: Cursor

* fix: add prepushScript to run-context API response, fix UI separator

Include prepushScript in the settings returned by the run-context
endpoint so the hook actually fires in production. Also fix the
separator pattern in AgentSettings to match the existing convention
(spacer + hr + spacer instead of margin).

Made-with: Cursor

mcp/server.ts

@@ -135,6 +135,7 @@ export interface ToolContext {
   apiToken: string;
   modes: Mode[];
   postCheckoutScript: string | null;
+  prepushScript: string | null;
   prApproveEnabled: boolean;
   modeInstructions: Record<string, string>;
   toolState: ToolState;