Split Altinity Cloud MCP gateway from local altinity-mcp  #133

The existing altinity-mcp binary serves local/single-cluster use cases: stdio, single ClickHouse target, and legacy HTTP/JWE/OpenAPI behavior.

Altinity Cloud needs a narrower gateway binary:

• HTTP streamable transport only
• OAuth required
• no stdio/SSE
• no JWE token routing
• no OpenAPI
• multicluster routing via /mcp/{cluster}
• per-token/per-cluster dynamic tool catalog cache

This avoids adding many mutually exclusive runtime modes to the current binary and keeps local usage stable.
Possibly, we need to strip the OAuth functionality from "non-cloud" binary, too.