feat(FN-2160): add push-after-merge remote sync workflow

- Add project settings for pushAfterMerge and pushRemote with defaults and typed merge result fields for push status/errors
- Implement post-merge remote sync in the merger with pull --rebase, auto/AI conflict resolution, and one non-fast-forward retry before push
- Expose push-after-merge controls in Settings modal with conditional Push Remote input and coverage for desktop/mobile save flows
- Document the new settings in the settings reference and stabilize CLI cross-build help test timeout

packages/core/src/settings-schema.ts

@@ -63,6 +63,8 @@ export const DEFAULT_PROJECT_SETTINGS = {
   groupOverlappingFiles: true,
   autoMerge: true,
   mergeStrategy: "direct",
+  pushAfterMerge: false,
+  pushRemote: "origin",
   worktreeInitCommand: undefined,
   testCommand: undefined,
   buildCommand: undefined,