* Fix daemon hang on Linux caused by waitpid(-1) race condition
Fixes#1035
The SIGCHLD handler added in v0.22.3 called `waitpid(-1, WNOHANG)` to reap zombie Chrome processes. This races with Rust's `Child::try_wait()` / `Child::wait()` because `waitpid(-1)` reaps *any* child in the process, stealing the exit status before the `Child` handle can collect it. The result is `ECHILD` errors in `BrowserManager::has_process_exited()` and `ChromeProcess::kill()`, leaving the daemon in a broken state that manifests as indefinite hangs on Linux servers.
The fix removes the global SIGCHLD handler and `reap_children()` function entirely. Instead, the existing 500ms drain interval now checks `mgr.has_process_exited()` (which delegates to `Child::try_wait()`) for targeted, race-free crash detection. When Chrome is detected as crashed, the `BrowserManager` is closed and daemon state is reset.
## Changes
- Removed `SIGCHLD` signal handler and `reap_children()` from the Unix daemon event loop
- Enhanced the drain interval to detect Chrome crashes via `has_process_exited()` and clean up state
- Added 3 regression tests:
- Static source scan that fails if `waitpid(-1)` is re-introduced in production code
- `try_wait()` correctness test for exit detection without a SIGCHLD handler
- Kill detection test simulating a Chrome crash
* fmt
Chris Tate
7b4b124e7f