orpc-v2: host handlers, OpenAPI 3.1.1 pin, and MCP tool generation

Ticket ID: B5

Parent

#248 — orpc-v2: consolidate fork into everything-dev and migrate platform to oRPC v2 + Effect 4 (epic)

What to build

Stage B, step 5: migrate the host to oRPC v2. The host's API route handlers live in host/src/routes/api.ts (the plan doc's claim that they live in program.ts is wrong) and need:

• Updated RPCHandler wiring; the interceptors option carries over unchanged (the doc's routingInterceptors/transportInterceptors rename does not apply).
• The ZodToJsonSchemaConverter import path update and the OpenAPIReferencePlugin rename per the v2 migration guide.
• The OpenAPI generator pinned to version: '3.1.1' — v2 defaults to 3.2.0 and MCP tool generation requires 3.1.
• The MCP service (tools generated from the OpenAPI spec) verified end-to-end.

Acceptance criteria

• Host serves identical REST/RPC paths (spec diff vs pre-migration, ignoring the OAS version field)
• OpenAPI spec generated at 3.1.1; /api docs render; MCP tools generate and invoke
• Host vitest suite green

Blocked by

• #259 — createPlugin restructure
• #260 — migrate all six contracts to the v2 route builder

Start with host/src/routes/api.ts and the oRPC v2 migration guide, then inspect the host's OpenAPI and MCP integration. Compare the generated spec with the pre-migration version and run the host vitest suite; done means identical paths, OpenAPI 3.1.1 docs, and MCP tools that generate and invoke successfully.