refactor(pi): type action ids with Pi's branded id types

[eersnington]

Pi's ids are numbers with a compile-time brand (Id<"conversation">, Id<"submission">, ...). Our actions already returned branded ids, but took number and cast it back 13 times. A client could pass a SubmissionId where a ConversationId belongs and still compile.

-abortSubmission: (c, id: number, conversationId?: number) =>
-	harness.abortSubmission(id as SubmissionId, context, conversationId as ConversationId | undefined)
+abortSubmission: (c, id: SubmissionId, conversationId?: ConversationId) =>
+	harness.abortSubmission(id, context, conversationId)

• Every action takes ConversationId, SubmissionId, TaskId, or EntryId, and every id cast is gone, also in requireConversation, requireSubmission, and requireTask.
• PiPromptOptions.conversationId, the stored WatchSpec, and the pi.events, pi.view, and pi.doc frames carry a ConversationId.
• Nothing changes on the wire. Clients pass back the ids they get from responses; a literal number needs ROOT_CONVERSATION_ID or an id from a response.

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This is part 6 of 9 in a stack:

•  9  docs(agents): type the React example's root id as ConversationId #346
•  8  feat(pi): prefix Pi Durable's tables in actor sqlite #345
•  7  chore(pi): bump and test Pi Durable 1.1.0 #344
•  6  refactor(pi): type action ids with Pi's branded id types #343 👈
•  5  refactor(sandbox-adapter): simplify sandboxEnv #342
•  4  refactor(pi): move databaseEnv into pi and version pi_file #341
•  3  fix(sandbox-adapter): stop waiting on aborted Daytona exec #340
•  2  fix(sandbox-adapter): stop Pi env calls when the run aborts #339
•  1  fix(pi): read an app credential with one source call #338