Resolve const-block conflict in openai_gateway_grok_cache.go:
keep #4590's client tool cache constants, drop grokFreeRolling24hTokenLimit
(moved to pkg/xai as IsGrokFreeRolling24hTokenLimit with legacy 2M support).
Round-trip Grok encrypted reasoning via Anthropic thinking.signature and
seed cache identity from Claude Code session IDs, so multi-turn /v1/messages
traffic can hit xAI prompt cache more like CLIProxyAPI. Also strip invalid
encrypted_content and retry on the Messages path when decrypt fails after
account switches.
Reuse applyGrokFreeMessagesFunctionToolCacheRoute on native /v1/responses
and the Grok WS HTTP bridge so Free OAuth requests with client function
tools get the same mixed-tools cache route as the Messages bridge
(append/convert web_search and x_search).
Also dedupe: Grok Build already declares function tools named web_search,
so naive append caused "Duplicate tool names: web_search". Convert those
function entries to native tool types and skip duplicates.
Only Free OAuth accounts (isKnownGrokFreeAccount); paid/unknown unchanged.
Edison42