Add BigTreeTech Knomi v2 board support - #41

Summary

• Adds a BSP and build variant (PRINTSPHERE_HW_VARIANT=knomi_v2) for BigTreeTech Knomi v2 (ESP32-S3, GC9A01 ×ばつ240, CST816S).
• Adapts UI layout/fonts for ×ばつ240, fixes GC9A01 MADCTL rotation in the Knomi BSP, and skips the UTF-8 BOM in HMS error_lookup.tsv so Klartext lookups work again.
• Documents Knomi build/packaging (docs/Build, release/knomi_v2/README.md, NOTICE.md) and extends package_release.ps1 / flash installer hooks for the new variant.

Notes for review

• Community contribution based on v1.6.2 from a fork of this repo.
• Prebuilt Knomi firmware (full + OTA) is published separately here (not part of this PR): https://github.com/forbidden-kiwi/PrintSphere-knomi/releases/tag/v1.6.2-knomi_v2
• README.md was adjusted for the fork (hardware table + install links). Happy to trim or rework that part to match upstream docs style.
• Existing AMOLED 1.75" / LCD 2.8c paths should remain the non-Knomi code paths.

Test plan

• idf.py -B build-knomi_v2 -D PRINTSPHERE_HW_VARIANT=knomi_v2 reconfigure build
• Factory-flash Knomi full image; confirm display orientation and touch
• Verify AMS / job preview / camera pages on ×ばつ240
• Confirm HMS Klartext for a known code (e.g. AMS drying) no longer shows only the raw HMS id
• Sanity-build AMOLED and/or LCD variant to ensure no regression
• Package with tools/package_release.ps1 (or Knomi-only packaging) and spot-check outputs