milestone 29: activity — history, live and policy simulation on one surface

query log, live and lookup merge into /activity. history filters live
in the url, so a pasted link or back/forward reproduces the exact
view; the result column separates servfail and nxdomain from success
in the list. live is follow-by-default with freeze, and a streamed
row opens its in-memory provenance detail — no correlation invented
for rows sqlite has not written. lookup survives as the current
policy simulation under /activity/test. investigation links carry
absolute bounds, and the diagnostics page now honors since/until
instead of ignoring them. the old routes are gone without aliases.

admin/src/features/activity/fakeEventSource.ts

@@ -0,0 +1,41 @@
+import { EVENT_SOURCE_CLOSED, type EventSourceLike } from "./useLiveQueries";
+
+const CONNECTING = 0;
+const OPEN = 1;
+
+/** Test double for the injected EventSource constructor. */
+export class FakeEventSource implements EventSourceLike {
+	readonly url: string;
+	closed = false;
+	readyState: number = CONNECTING;
+	private listeners = new Map<string, Array<(event: { data?: unknown }) => void>>();
+
+	constructor(url: string) {
+		this.url = url;
+	}
+
+	addEventListener(type: string, listener: (event: { data?: unknown }) => void): void {
+		const existing = this.listeners.get(type) ?? [];
+		existing.push(listener);
+		this.listeners.set(type, existing);
+	}
+
+	close(): void {
+		this.closed = true;
+		this.readyState = EVENT_SOURCE_CLOSED;
+	}
+
+	emit(type: string, event: { data?: unknown } = {}): void {
+		if (type === "open") this.readyState = OPEN;
+		for (const listener of this.listeners.get(type) ?? []) listener(event);
+	}
+
+	/**
+	 * A non-200 response: the browser closes the source, then dispatches one
+	 * error event and never retries.
+	 */
+	failFatal(): void {
+		this.readyState = EVENT_SOURCE_CLOSED;
+		this.emit("error");
+	}
+}