feat(permissions): YOLO mode, global-only settings, runtime /yolo with dialog gate

[alecuba16]

Second split from #388 (bang commands landed as #404). YOLO mode only, branched off main, no shared payload with the other splits.

What this adds

• config.yolo_mode ("yoloMode" in settings.json): when true, the effective permission mode is BypassPermissions at startup.
• /yolo [on|off] runtime toggle, gated by the existing BypassPermissionsModeDialog.

Security review points addressed

1. Global-only merge (the blocker). Settings::merge pins yolo_mode: base.config.yolo_mode, the same pattern as skip_dangerous_mode_permission_prompt. A cloned repo shipping {"config":{"yoloMode":true}} cannot flip bypassPermissions on; a global false cannot be overridden by a project file. Covered by yolo_mode_is_global_only_in_merge plus a tempdir test (project_settings_cannot_enable_yolo_mode) that writes an isolated CLAURST_HOME global and a project settings file with yoloMode: true and asserts the merged result is off.
2. Root/sudo guard kept. The yoloMode startup path runs the same Uid::effective().is_root() bail as --dangerously-skip-permissions. The guard is not skipped.
3. Runtime /yolo goes through the dialog. /yolo on shows BypassPermissionsModeDialog first (yolo_pending flag distinguishes the runtime toggle from the startup gate). Accepting switches the mode; declining cancels the toggle and dismisses the dialog without exiting.
4. /yolo off does not hard-set Default. The mode active before /yolo on is remembered and restored, so plan/acceptEdits sessions survive a YOLO round-trip.
5. No test writes the real settings. Runtime /yolo is session-only (no save_sync in its path). The tempdir test isolates CLAURST_HOME so cargo test never touches the developer settings.json.

Tests

• 3 core tests: global-only merge both directions, project-cannot-enable (tempdir), camelCase JSON roundtrip.
• 5 TUI tests: accept activates, decline cancels without exit, off restores previous mode (plan round-trip), off restores Default, toggle shows dialog.

cargo check --workspace, cargo clippy --workspace --all-targets -- -D warnings, and both test suites pass. The settings_screen count test failure on main is pre-existing and unrelated.

Docs

docs/commands.md (CRLF preserved) documents /yolo; docs/configuration.md documents yolo_mode with the global-only note.