Fix code review issues in process management refactor

- Add pwd validation in Process.launch() to prevent crashes
- Fix psutil returncode handling (use wait() return value, not returncode attr)
- Add None check for proc.pid in cleanup_stale_running()
- Add stale process cleanup in Orchestrator.is_running()
- Ensure orchestrator process_type is correctly set to ORCHESTRATOR
- Fix KeyboardInterrupt handling (exit code 0 for graceful shutdown)
- Throttle cleanup_stale_running() to once per 30 seconds for performance
- Fix worker process_type to use TypeChoices.WORKER consistently
- Fix get_running_workers() API to return list of dicts (not Process objects)
- Only delete PID files after successful kill or confirmed stale
- Fix migration index names to match between SQL and Django state
- Remove db_index=True from process_type (index created manually)
- Update documentation to reflect actual implementation
- Add explanatory comments to empty except blocks
- Fix exit codes to use Unix convention (128 + signal number)

Co-authored-by: Nick Sweeting <pirate@users.noreply.github.com>

archivebox/crawls/models.py

@@ -424,8 +424,10 @@ class Crawl(ModelWithOutputDir, ModelWithConfig, ModelWithHealthStats, ModelWith
         if self.OUTPUT_DIR.exists():
             for pid_file in self.OUTPUT_DIR.glob('**/*.pid'):
                 cmd_file = pid_file.parent / 'cmd.sh'
-                safe_kill_process(pid_file, cmd_file)
-                pid_file.unlink(missing_ok=True)
+                # Only delete PID file if kill succeeded or process is already dead
+                killed = safe_kill_process(pid_file, cmd_file)
+                if killed or not pid_file.exists():
+                    pid_file.unlink(missing_ok=True)
 
         # Run on_CrawlEnd hooks
         from archivebox.config.configset import get_config