orpc-v2: plugin router merge helper, drop /things passthrough, typed PluginsClient entries

Ticket ID: P2

Parent

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

What to build

Prefactor: give every-plugin a router-merge helper so the api can merge each plugin's router into the base router directly, and remove the /things passthrough indirection in the api's router assembly. The PluginsClient type gains per-plugin typed router entries, so plugin routes are reachable through the merged router with full type inference — no more generic passthrough calls.

Wire-compatible: existing route paths, responses, and the host's plugin-loading flow are unchanged.

Acceptance criteria

• every-plugin exposes the merge helper with unit tests
• /things passthrough removed; the same plugin routes served through the merged router with identical paths/responses
• PluginsClient exposes typed per-plugin router entries; workspace typecheck green
• api test suite + regression tests green

Blocked by

• #250 — merge citynode.app into everything-dev main

Start in the every-plugin router exports and the api router assembly described in the ticket; inspect how PluginsClient is currently typed and how /things passthrough calls are wired. Add and unit-test the merge helper, then run the workspace typecheck, api test suite, and regression tests. Done means identical route paths and responses, typed per-plugin entries, and all checks green; #250 must be resolved first.