Sync zen42 keymap with lily58 primary layout

[cbxm]

Summary

• Syncs the Zen42 keymap to match the Lily58 (primary board)
• Fixes homerow mod tapping term, cross-hand modifier pattern, dance behavior placement
• Rearranges board layers to match Lily58 layout (BT nav + media on active hand, disconnects on opposite)
• Adds L_mo_keeb combo (backspace thumb + far-left homerow → boardLeft layer)

Test Plan

• Build firmware via GitHub Actions CI
• Flash both halves and verify base layer typing
• Test homerow mods (hold A/S/D/F and J/K/L/; for modifiers)
• Test board layers (hold symbolsLeft + NumRight to activate conditional layer)
• Test L_mo_keeb combo (press backspace thumb + far-left homerow key simultaneously)
• Verify BT controls work on both boardLeft and boardRight