Hotfix C4: add invokeInternalTool to worker-message RPC method enum

Production bug — as soon as the CEO agent tries to call the hire_agent
or file_approval internal tool introduced by C4 (e2c839b..03864f3),
the main process spams:

  [error] [worker] invalid message payload ZodError: ...

with all seven discriminant branches failing. Every branch reports
'invalid_value' on 'type' because zod's discriminated-union validator
walks every variant when the discriminant does not match any
literal — which happens because the worker sent
`{ type: "rpc-request", method: "invokeInternalTool", ... }` and the
'rpc-request' branch's `method: z.enum([...])` only listed five
methods: persistMessage / prepareRun / beforeToolCall / afterToolCall
/ transformContext. 'invokeInternalTool' was missing.

Root cause: C4 added the RPC method on both sides of the fence —
worker-side caller (hire-agent-tool.ts:133, file-approval-tool.ts:115)
and main-side handler (runtime-bridge.ts:565, RpcMethod TS union at
line 77) — but forgot to register it in the zod validation schema
at worker/entry/types.ts that sits between them. The TS union type
would have caught it at compile time if the enum were the single
source of truth; right now the enum is duplicated as a zod literal
list + a TS union, and C5's compile-time hook contract only covers
pi's own hooks, not the RPC message envelope.

Fix: add "invokeInternalTool" to the zod enum. One line.

Follow-up proposal C5-followup: unify the two duplicated enum
definitions by either (a) deriving the TS union from the zod
schema via z.infer, or (b) making runtime-bridge.ts import the
enum values from worker/entry/types.ts so adding an RPC method
requires touching exactly one place. This will be documented in
docs/proposals/ once the hotfix lands and the app is known to
work end-to-end again. Scope for that cleanup is small (one file
edit + one type move) but out of scope for this hotfix because the
user is currently unable to run the CEO bootstrap.

typecheck green, 529 unit tests green, 8/8 eval green.

src/main/worker/entry/types.ts

@@ -53,6 +53,7 @@ export const workerMessageSchema = z.union([
       "beforeToolCall",
       "afterToolCall",
       "transformContext",
+      "invokeInternalTool",
     ]),
     payload: z.unknown(),
   }),