feat(rpc): transport, server, client, http, mounting, docs (Tasks 5-11)

Brings the uncommitted body of work under version control so it cannot be
lost. Gates are green: 152 tests pass across rpc/router/dev-server,
typecheck, lint, format and check:public-api all clean.

NOT YET REVIEWED. None of Tasks 5-11 has had an independent task review, and
Task 4's second fix round was never re-reviewed either.

Known gaps against the plan, recorded here rather than discovered later:
- packages/rpc/test/{transport,server,client}.test.ts are ABSENT. The plan
  required a test file for each. server.ts holds the fail-closed identity and
  permission checks and currently has no direct coverage at all.
- rpc-endpoint.test.ts has 3 tests where the plan specified 9. Missing:
  unknown service, non-POST, malformed body, non-rpc passthrough, and the
  isInternalCaller sweep. This is the task where a reachable
  /__wrnexus/rpc/* makes every permission check in the workspace bypassable.
- http.test.ts has 3 of 7; integration.test.ts 2 of 3;
  services-discovery.test.ts 1 of 4.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/rpc/src/index.ts

@@ -30,3 +30,17 @@ export {
   rpcSecret,
 } from "./identity.ts";
 export type { ExportOptions, ImportOptions, SubjectContext } from "./identity.ts";
+
+export { inProcessTransport } from "./transport.ts";
+export type { CallOptions, InProcessHandler, RpcTarget, Transport } from "./transport.ts";
+export { implement } from "./server.ts";
+export type {
+  HandlerContext,
+  ImplementOptions,
+  ServiceHandlers,
+  ServiceImplementation,
+} from "./server.ts";
+export { serviceClient } from "./client.ts";
+export type { ServiceClient, ServiceClientOptions } from "./client.ts";
+export { RPC_INTERNAL_HEADER, RPC_PATH_PREFIX, httpTransport, rpcPath } from "./http.ts";
+export type { HttpTransportOptions } from "./http.ts";