fix: support the full Mini Flip volume range

[dime-online]

Summary

• keep the Mini Flip adapter on PyUI's existing 0–100 volume contract
• map each five-point PyUI step to one of Sprig's 0–20 hardware levels
• correct the two fallback paths to sprig/scripts/helperFunctions.sh

Root cause

SystemConfig exposes the stored 0–20 value to PyUI as 0–100, and the settings UI displays that value divided by five. The Sprig Mini adapter was the only layer clamping it to 0–50 and then scaling it back to 0–20. That capped Settings at 10, made a menu adjustment span two hardware levels, and could collapse a side-button value above 10 during startup or the next menu adjustment.

Validation

• syntax check
• all 21 canonical levels and all 42 left/right transitions
• lower and upper clamps, mute boundary, direct procfs writes, and both shell fallbacks
• full 0–20 sweep on Miyoo Mini Flip hardware
• confirmed 20 → 19, side-key/menu interoperability, and persistence after reboot

Fixes #237