CTX7-2712: Add single Search API MCP mode

[fahreddinozcan]

Summary

• adds an opt-in single MCP tool mode backed by GET /api/v2/context/search
• exposes one query-docs tool with query, optional libraries: string[], and optional version
• keeps the existing two-tool mode as the default
• preserves fuzzy names and exact Context7 IDs in one non-duplicated library list

Tool flow

1. The agent sends the complete question once, retaining every named product, version, and concept.
2. Optional library hints are forwarded together in one backend request; they are not split into parallel public tool calls.
3. The backend selects and searches bounded library namespaces, merges their evidence, and returns the chosen library IDs with the documentation.
4. Terminal misses remain successful MCP responses with guidance not to repeat the same request. Explicit transient failures are MCP errors and may be retried once later.

The endpoint algorithm and benchmark rationale are documented in:

• https://github.com/upstash/context7app/pull/1163
• https://github.com/upstash/context7benchmark/pull/19

Verification

• merged current master and resolved the telemetry overlap without removing either feature
• type-check passed
• lint passed
• build passed
• 137/137 tests passed locally
• GitHub test check passed

Closes CTX7-2712

[linear-code]

CTX7-2712