Audit and remove process.exit() calls from commands and command handlers

[acreeger]

Summary

Command handlers use process.exit() throughout, which causes two problems:

1. Telemetry bug (immediate): process.exit() kills the process before PostHog's async HTTP requests complete, causing telemetry events (especially loom.finished) to be silently dropped. A workaround of calling TelemetryService.getInstance().shutdown() before each exit has been added in cli.ts, but it's fragile and easy to forget.

2. Reusability (future): Commands should be callable directly by other wrappers (e.g., a VS Code extension) without process.exit() terminating the host process.

Affected files

src/cli.ts — ~10 process.exit(0) calls in command action handlers (workaround shutdown calls added)

src/commands/finish.ts:185 — process.exit(1) in checkForChildLooms
src/commands/start.ts:311 — process.exit(0)
src/commands/contribute.ts:238 — process.exit(0)
src/commands/update.ts — multiple process.exit(1) and process.exit(code ?? 0)

Task

• Remove all process.exit(0) calls from command action handlers in cli.ts — let commands return naturally so the top-level program.parseAsync() flow handles shutdown
• Remove all process.exit() calls from command classes — commands should throw errors or return, never exit
• Convert process.exit(1) error paths to thrown errors, letting the top-level catch handle exit codes
• Handle special exit codes (e.g., 130 for UserAbortedCommitError) via typed errors with exit code properties
• Remove the TelemetryService.shutdown() workaround calls once exits are removed
• Verify no open handles prevent clean process exit after commands complete
• Update tests that mock process.exit behavior