fix: track in-flight requests by id; handle llama-swap upsert/remove events

llama-swap emits inflight events with operation 'upsert' (a single request,
re-emitted as elapsed_ms updates) and id-only 'remove' events. The decoder
ignored 'upsert' and dropped every id-only remove, so the tracker only ever
reflected the connect-time snapshot and the count got stuck (e.g. at '1').

The tracker now keys in-flight state by request id (snapshot/add replace by
id; remove deletes by id), and the decoder normalizes 'upsert' to 'add' and
extracts the id from bare removes.

src/lib/event-feed.ts

@@ -9,6 +9,13 @@ export function decodeEvent(msg: SseMessage): FeedEvent | null {
     const inner = JSON.parse(outer.data) as Record<string, unknown>;
 
     if (outer.type === "inflight") {
+      const operation = inner.operation as string;
+      if (operation === "remove") {
+        const id = typeof inner.id === "string" ? inner.id : undefined;
+        if (id) return { type: "inflight", operation: "remove", id };
+        return null;
+      }
+      if (operation !== "snapshot" && operation !== "upsert" && operation !== "add") return null;
       const requests: InflightRequest[] = Array.isArray(inner.requests)
         ? (inner.requests as InflightRequest[])
         : Array.isArray(inner.request)
@@ -18,7 +25,7 @@ export function decodeEvent(msg: SseMessage): FeedEvent | null {
             : [];
       return {
         type: "inflight",
-        operation: inner.operation as "snapshot" | "add" | "remove",
+        operation: operation === "snapshot" ? "snapshot" : "add",
         requests,
       };
     }