perf(activity): page, summarize and reconcile activity history in Main by index

Schema 57 rebuilds activity_history_records with order_seq (newer = larger;
a move to the front assigns a new maximum) and stored generated columns
(record_id, occurrence, status, status_group, kind, request_id,
conversation_id, project_id, created_at) with indexes. The order is migrated
from record_order_json exactly; legacy duplicates keep their occurrence and
only the first is shown. record_order_json is no longer written.

ActivityHistoryRepository owns the SQL: page({before, limit <= 500, filter,
projectId, conversationId}) newest first by index, summary() with the counts
and conversation titles/status the Activity page derived from the full list,
reconcile() joined with tasks with a renderer-localized detail line, update()
applied directly in SQL without reading the history, replace() for the
legacy migration, clear(). New activity-history:page/summary/reconcile IPC
with zod validation; page and summary run on the readonly worker.
perf:main measures 24,000 records: startup load 106 ms on Main (14 MB) ->
first page + summary 13.5 ms on the worker (0.6 ms loop block, 114 KB).

src/renderer/src/App.test.tsx

@@ -193,7 +193,11 @@ vi.mock("./TerminalPanel", () => ({
 
 import App from "./App";
 import { ACTIVITY_STORAGE_KEY, type ActivityRecord } from "./activity-store";
-import { applyActivityChanges } from "../../shared/activity-history-reference";
+import {
+  applyActivityChanges,
+  referenceActivityPage,
+  referenceActivitySummary,
+} from "../../shared/activity-history-reference";
 import type { ActivityHistoryUpdate } from "../../shared/assistant-contracts";
 import { changeUiLocale } from "./i18n";
 import { UiLocaleProvider } from "./i18n/UiLocaleProvider";
@@ -689,6 +693,10 @@ const api: DesktopApi & RuntimeNativeClientApi = {
     clear: vi.fn(async () => {
       savedActivity = [];
     }),
+    page: vi.fn(async (request) => referenceActivityPage(savedActivity, request)),
+    summary: vi.fn(async (request) =>
+      referenceActivitySummary(savedActivity, request.conversationIds)),
+    reconcile: vi.fn(async () => 0),
   },
   usage: {
     getTokenSummary: vi.fn(async () => ({