feat: prepare GeaconSolstice ZMK 0.4 validation baseline

[te9no]

Summary

• prepare GeaconSolstice on the pinned ZMK 0.4 baseline used by Polaris and MKB2 validation
• pin every active west dependency to a full commit SHA
• migrate the right PMW3610 to the Zephyr 4.1 built-in input driver and bindings
• keep Studio RPC, USB logging, CDC UF2 entry, and battery oversampling on the left split central only
• keep the right split peripheral free of USB logging and Studio transport snippets
• validate shared ZMK 0.4 fixes for dongle display and temp-layer processing

CI validation

• full matrix run: 7/7 jobs passed
• all 5 firmware targets passed: US/JIS left and right plus settings reset
• build compatibility only; hardware validation is still required

Shared module PRs

• fix: support LVGL 9 on ZMK 0.4 zmk-dongle-display#3: LVGL 9 and endpoint API migration
• fix: support ZMK 0.4 layer API yamaryu211/zmk-input-processor-temp-layer-threshold#2: ZMK 0.4 layer API

Validation policy

This PR must remain draft and must not be merged into main after CI alone. Hardware testing is required first; see docs/zmk-0.4-validation.md.

Hardware checks required

• US and JIS split pairing and normal key input
• left analog stick and right PMW3610
• runtime input processors and Studio RPC
• dongle display and RGB LED widget
• CDC UF2 entry and USB logging on the left
• battery reporting/oversampling, idle sleep, and reconnect

[te9no]

Superseded by consolidated PR #4, hardware-validated and merged into zmk-0.4.