feat: Add Form Editor for config.h with QMK define settings

[yoichiro]

Summary

• Add a Form Editor tab for config.h files in the workbench, matching the keyboard.json editor pattern
• Create ConfigHParser service for parsing/generating #define directives (preserves comments, formatting, and non-define lines)
• Create ConfigHSettingsPanel with 6 vertical tabs: Tap/Hold, Mouse Keys, Combo, Auto Shift, One Shot, Leader Key
• Implement 2-way binding with 500ms debounce auto-apply (same pattern as keyboard.json Form Editor)
• Add helper text descriptions for all fields (switches and numeric inputs)
• Show parse error message when config.h content is invalid
• Add Japanese translations for all UI labels and descriptions

Test plan

• Open config.h → verify Code Editor and Form Editor tabs appear
• Switch to Form Editor → verify Tap/Hold tab displays with all fields
• Set TAPPING_TERM to 200 → switch to Code Editor → verify #define TAPPING_TERM 200 appears
• Toggle PERMISSIVE_HOLD on → switch to Code Editor → verify #define PERMISSIVE_HOLD appears
• Toggle PERMISSIVE_HOLD off → switch to Code Editor → verify the define is removed
• Edit config.h in Code Editor → switch to Form Editor → verify values are reflected
• Break config.h syntax in Code Editor → switch to Form Editor → verify error message shown
• Verify all 6 tabs (Tap/Hold, Mouse Keys, Combo, Auto Shift, One Shot, Leader Key) render correctly
• Verify helper text descriptions appear for all switches and numeric inputs
• Verify Japanese locale displays correctly
• Run ConfigHParser tests (19 tests)

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