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/engineer.ts

@@ -0,0 +1,21 @@
+/**
+ * What PodMan currently believes an engineer is doing, derived from vision on
+ * their shared screen and refreshed every few seconds. This is the live,
+ * pre-push signal that the GitHub API cannot see.
+ */
+export interface EngineerContext {
+  engineerId: string;
+  podId: string;
+  /** File path PodMan sees open/active in the editor, e.g. "src/auth.ts". */
+  currentFile?: string;
+  /** Function/class/symbol being edited, if vision can resolve it. */
+  currentSymbol?: string;
+  /** Higher-level feature/action inferred from the screen. */
+  activity?: string;
+  /** Whether the screen shows uncommitted/unpushed changes (gutter/diff). */
+  hasUnpushedChanges?: boolean;
+  /** 0–1 confidence in this read of the screen. */
+  confidence: number;
+  /** ISO timestamp of the observation this context came from. */
+  observedAt: string;
+}