Add Q8 Pro support to 2025q3

[milan-stoj]

Description

Add Keychron Q8 Pro support with ANSI encoder and ISO encoder variants.

This PR introduces:

• New keyboard definition for Keychron Q8 Pro
• ANSI encoder and ISO encoder keyboard targets
• Default keymaps for both variants
• VIA JSON files for both variants
• Board-level config, MCU/HAL config, and build rules needed for wireless + RGB + encoder support

Validation performed:

• qmk compile -kb keychron/q8_pro/ansi_encoder -km default
• qmk compile -kb keychron/q8_pro/iso_encoder -km default
• qmk lint -kb keychron/q8_pro/ansi_encoder -km default
• qmk lint -kb keychron/q8_pro/iso_encoder -km default

All checks passed.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• N/A

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).