feat: fuse engineer_states git truth into collision detector

Add getGitStates(podId) to db.ts — queries the engineer_states collection
written by scripts/podman-agent.mjs and returns a map keyed by engineer name.

In PodMan.onScreenFrame(), fuse before detectCollisions(): if an engineer has
changedFiles in engineer_states, force hasUnpushedChanges=true on their context.
This overrides Gemini vision's unreliable pixel-based guess with deterministic
local git state — preventing the money-moment collision from silently not firing.

Key assumption: LiveKit participant identity matches the --name arg used when
running the git watcher (e.g. identity "alice" → --name alice).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AaCFWMkYQmTcuPsxaaACft

backend/src/memory/db.ts

@@ -43,6 +43,38 @@ export async function collections(): Promise<PodCollections> {
   };
 }
 
+export interface GitState {
+  changedFiles: string[];
+  branch: string | null;
+  recentCommit: string | null;
+  gitUpdatedAt: Date | null;
+}
+
+/** Fetch latest git state per engineer for a pod from the engineer_states collection.
+ *  Returns a map keyed by engineer name (matches --name arg used in podman-agent.mjs). */
+export async function getGitStates(podId: string): Promise<Map<string, GitState>> {
+  const db = await getDb();
+  const col = db.collection<{
+    _id: string;
+    name: string;
+    changedFiles?: string[];
+    branch?: string | null;
+    recentCommit?: string | null;
+    gitUpdatedAt?: Date;
+  }>('engineer_states');
+  const docs = await col.find({ podId }).toArray();
+  const map = new Map<string, GitState>();
+  for (const doc of docs) {
+    map.set(doc.name, {
+      changedFiles: doc.changedFiles ?? [],
+      branch: doc.branch ?? null,
+      recentCommit: doc.recentCommit ?? null,
+      gitUpdatedAt: doc.gitUpdatedAt ?? null,
+    });
+  }
+  return map;
+}
+
 /** Connect, verify reachability, and create helpful indexes. Call once on startup. */
 export async function initMemory(): Promise<void> {
   const db = await getDb();