feat(exit-codes): Unix-standard process exit codes for all error types

[jackwener]

Summary

opencli now returns meaningful Unix process exit codes, making it a proper citizen of shell pipelines and CI scripts.

Exit code	Meaning	Error type
0	Success	—
1	Generic / unexpected error	CliError, unknown errors
2	Argument / usage error	ArgumentError
66	No result / not found	EmptyResultError, SelectorError, untyped not-found errors
69	Service unavailable	BrowserConnectError, AdapterLoadError
77	Auth required / permission denied	AuthRequiredError, untyped auth errors
78	Configuration error	ConfigError
124	Timeout	TimeoutError
130	Interrupted (Ctrl-C)	unchanged, tui.ts SIGINT handler

Implementation

• src/errors.ts: Added EXIT_CODES constant table (single source of truth, documented in JSDoc). Added exitCode: ExitCode field to CliError base class — each subclass passes its code via super(), so there's no external mapping to maintain.
• src/commanderAdapter.ts: Added resolveExitCode(err) that reads err.exitCode for CliError instances, and falls back to pattern-matching message text for untyped adapter errors (auth pattern → 77, not-found → 66, else → 1). The catch block now calls resolveExitCode instead of hardcoding 1.

Usage examples

# Detect auth failure vs browser not running
opencli github issues 2>/dev/null
case $? in
  0)   echo "ok" ;;
  69)  echo "start the daemon first" ;;
  77)  opencli github auth && opencli github issues ;;
  *)   echo "error $?" ;;
esac

# CI: fail fast on bad args, ignore empty results
opencli spotify search "$(cat query.txt)" || [ $? -eq 66 ]

Test plan

• opencli spotify auth without credentials → exit 78 (ConfigError)
• opencli github issues --bad-arg → exit 2 (ArgumentError)
• Run with no daemon running → exit 69 (BrowserConnectError)
• Normal successful command → exit 0