Handle KeyboardInterrupt gracefully in CLI

[holmboe]

Summary

• Add exception handling for KeyboardInterrupt (Ctrl+C) to provide a clean exit instead of displaying a full traceback
• Improves user experience when cancelling long-running operations like network requests

Changes

• Catch KeyboardInterrupt in cli_entrypoint() function
• Display "Operation cancelled by user." message to stderr
• Exit with code 130 (standard Unix convention: 128 + SIGINT signal number 2)

Before

^CTraceback (most recent call last):
  File "/home/nn/code/github.com/dynamist/phabfive/.venv/bin/phabfive", line 10, in <module>
    sys.exit(cli_entrypoint())
  [... 50+ lines of traceback ...]
KeyboardInterrupt

After

^C
Operation cancelled by user.

Exit code: 130

Test Plan

• Tested with mock KeyboardInterrupt simulation
• Verified clean output message
• Verified exit code 130
• Confirmed other exceptions still propagate normally

🤖 Generated with Claude Code