fix(cursor): align Grok 4.7 context window to 256k/500k and drop unsupported max effort tier

Summary

In the Cursor provider catalog:

1. Grok 4.7 currently falls back to 200,000 context tokens because bare grok-4.7 is not explicitly declared in cursorProvider.models. Per Cursor/xAI documentation, Grok 4.7 has a 256k standard context window and a 500k extended context window.
2. GROK_47_EFFORT_TIERS in cursorAutoCatalog.ts includes max. Grok 4.7 only supports low, medium, high, and xhigh.

Fix

• Declare grok-4.7 (256k) and grok-4.7-500k (500k) in cursorProvider.models.
• Remove max from GROK_47_EFFORT_TIERS in cursorAutoCatalog.ts and ensure effort mapping matches GROK_47_EFFORTS.
• Update unit tests.