v1.2.0: music on satellites, song lookup over MCP, leaner build

• Nexus Orbit: the music can play on a PC or Pi running nexus-orbit
  (/api/orbit/ws, up to 3 satellites). Handoff at the current position,
  board resumes if the satellite drops, pauses during a voice session
  like local music. Output picker in the dashboard; "play it on the PC"
  by voice (music_output skill).
• Song lookup goes through the MCP server (device-only tools, hidden
  from Gemini); the board's own Invidious client stays as a fallback
  (CONFIG_WAVESHARE_INVIDIOUS_FALLBACK).
• USB network mode only with CONFIG_WAVESHARE_USB_NET (off by default):
  11.7 KB internal RAM and 44 KB flash back.
• Wi-Fi debugging tools removed (wifi-sniff, wifi-log, wifi-rx,
  wifi-mac, tuning.json).