feat(shared): add core domain types

Pod/Engineer, EngineerContext (live pre-push signal), Collision, and
Intervention — the type contract between frontend and backend.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

shared/src/pod.ts

@@ -0,0 +1,19 @@
+/** A pod is one room of engineers working together (one LiveKit room per pod). */
+export interface Pod {
+  id: string;
+  name: string;
+  /** GitHub repo the pod is working in, as "owner/name". */
+  repo: string;
+  members: Engineer[];
+  createdAt: string;
+}
+
+export interface Engineer {
+  id: string;
+  /** Display name PodMan uses when it speaks ("Karti and Yahya are both..."). */
+  name: string;
+  /** GitHub login, used to map vision context to GitHub state. */
+  githubLogin?: string;
+  /** LiveKit participant identity for this engineer in the pod room. */
+  participantId?: string;
+}