Google Provider Compatibility Docs

@robota-sdk/agent-provider-google remains available as a compatibility wrapper for existing imports and settings that still use the google provider profile.

Current Guidance

• New Gemini API code should use @robota-sdk/agent-provider-gemini.
• Existing GoogleProvider imports continue to work during migration.
• The canonical provider profile type is gemini; google remains accepted as an alias.

Documents

• Package README — migration guidance.
• SPEC.md — compatibility package contract and migration path.