Fix CLI to work without webapi extras

[JnyJny]

Summary

• Fixes CLI to work without webapi extras installed
• Resolves uvx --with busylight-for-humans busylight failure
• Maintains full functionality when webapi extras are installed

Problem

The CLI was failing when used via uvx --with busylight-for-humans busylight because it attempted to import busyserve_cli unconditionally, which depends on uvicorn from the optional [webapi] extras group. This created a hard dependency on webapi components even for basic light control operations.

Solution

Implemented conditional imports and import-time validation:

1. Conditional CLI registration in __main__.py:

   • Wrapped busyserve_cli import in try/except block
   • Only adds busyserve subcommand when webapi dependencies are available
   • Gracefully degrades when extras are missing

2. Import-time validation in busyserve.py:

   • Moved dependency check to import time
   • Provides clear error message with installation instructions
   • Prevents module loading when dependencies are missing

Changes Made

/src/busylight/__main__.py

• Removed unconditional import of busyserve_cli
• Added conditional import with try/except handling
• CLI gracefully excludes busyserve functionality when webapi extras unavailable

/src/busylight/busyserve.py

• Moved uvicorn import check to module level
• Converted runtime error to ImportError for proper exception handling
• Enhanced error message with clear installation instructions

Testing

• ✅ CLI works without webapi extras: uvx --with busylight-for-humans busylight --help
• ✅ CLI works with webapi extras: full busyserve functionality available
• ✅ Clear error messages guide users when extras needed
• ✅ No regression in existing functionality

User Impact

• Before: CLI failed completely without webapi extras installed
• After: CLI works for all light control operations; webapi features gracefully unavailable
• Users get clear guidance on installing extras when attempting to use web functionality
• Maintains backwards compatibility for existing installations with webapi extras

🤖 Generated with Claude Code

[JnyJny]

LGTM.