Allow users to create Gemini provider configurations without API key
and fill it in later. Split validation into two modes:
- validate_gemini_settings: Basic structure check (used when adding)
- validate_gemini_settings_strict: Full validation (used when switching)
This fixes the error 'Gemini config missing required field: GEMINI_API_KEY'
when trying to add Gemini providers from presets like PackyCode or Google.
Changes:
- Add validate_gemini_settings_strict for switching validation
- Update write_gemini_live to use strict validation
- Add comprehensive tests for both validation modes
a85f24f616