fix(mimicry): align cache_control, betas, and headers with CC 2.1.98 Proxyman capture

- cache_control: remove scope/ttl fields (CC sends only {type:"ephemeral"})
- betas: remove auto-include of advanced-tool-use and fast-mode (CC doesn't send them)
- betas: add advisor-tool-2026-03-01 (CC always sends it)
- headers: add x-client-request-id UUID per request

Constraint: Changes derived from actual Proxyman capture of CC 2.1.98 traffic
Confidence: high
Scope-risk: moderate