feat: Add Audio tab to keyboard.json Form Editor

[yoichiro]

Summary

• Add a dedicated Audio tab to the keyboard.json Form Editor with support for:
  • audio.pins — audio output pins (comma-separated text input)
  • audio.driver — driver selection (pwm_hardware, pwm_software, dac_basic, dac_additive)
  • audio.voices — enable multiple audio voices (with description)
  • audio.macro_beep — play beep on macro execution (with description)
• Rename Input tab to Encoder for clarity
• Reorder tabs: Audio (5) comes before Encoder (6)
• Add Japanese translations for all new labels and descriptions

Test plan

• Open keyboard.json → Form Editor → verify Audio tab appears between Lighting and Encoder
• Set audio pins to "C6" → switch to Code Editor → verify "audio": { "pins": ["C6"] } in JSON
• Select driver "pwm_hardware" → verify it appears in JSON
• Toggle Voices on → verify "voices": true in JSON
• Toggle Macro Beep on → verify "macro_beep": true in JSON
• Verify Voices and Macro Beep switches show description text
• Verify Encoder tab (formerly Input) still works correctly
• Verify Japanese locale displays correctly for Audio tab and descriptions

🤖 Generated with Claude Code