fix(search): apply the date range to server results client-side

from_ts/to_ts are not Matrix filter fields; the server dropped them, so
the range only worked for the local encrypted-room search. Stop sending
them and post-filter server results by origin_server_ts with the same
inclusive predicate. Unit-tested; docs corrected.

Fixes #13

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/message-search/useMessageSearch.test.ts

@@ -1,6 +1,11 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { filterGroupsByMsgType, filterGroupsByPinned, ResultGroup } from './useMessageSearch';
+import {
+  filterGroupsByDateRange,
+  filterGroupsByMsgType,
+  filterGroupsByPinned,
+  ResultGroup,
+} from './useMessageSearch';
 
 // Minimal ResultGroup/ResultItem fixtures — only the fields the filters read
 // (event.content.msgtype, event.event_id, group.roomId).
@@ -9,6 +14,11 @@ const item = (msgtype: string | undefined, eventId: string) => ({
   event: { event_id: eventId, content: msgtype === undefined ? {} : { msgtype } },
   context: {},
 });
+const tsItem = (eventId: string, ts: number) => ({
+  rank: 1,
+  event: { event_id: eventId, origin_server_ts: ts, content: {} },
+  context: {},
+});
 const mkGroups = (
   ...groups: { roomId: string; items: ReturnType<typeof item>[] }[]
 ): ResultGroup[] => groups as unknown as ResultGroup[];
@@ -48,6 +58,33 @@ test('filterGroupsByMsgType: ignores items with a non-string msgtype', () => {
   assert.equal(out[0].items[0].event.event_id, '$2');
 });
 
+test('filterGroupsByDateRange: no bounds returns groups unchanged', () => {
+  const groups = mkGroups({ roomId: '!r1', items: [tsItem('$1', 100)] });
+  assert.equal(filterGroupsByDateRange(groups, undefined, undefined), groups);
+});
+
+test('filterGroupsByDateRange: keeps only items within an inclusive range', () => {
+  const groups = mkGroups({
+    roomId: '!r1',
+    items: [tsItem('$1', 50), tsItem('$2', 100), tsItem('$3', 150), tsItem('$4', 200)],
+  });
+  const out = filterGroupsByDateRange(groups, 100, 150);
+  assert.deepEqual(
+    out[0].items.map((i) => i.event.event_id),
+    ['$2', '$3'],
+  );
+});
+
+test('filterGroupsByDateRange: drops groups left empty and supports one-sided bounds', () => {
+  const groups = mkGroups(
+    { roomId: '!r1', items: [tsItem('$1', 50)] },
+    { roomId: '!r2', items: [tsItem('$2', 500)] },
+  );
+  const out = filterGroupsByDateRange(groups, 100, undefined);
+  assert.equal(out.length, 1);
+  assert.equal(out[0].roomId, '!r2');
+});
+
 test('filterGroupsByPinned: disabled returns groups unchanged', () => {
   const groups = mkGroups({ roomId: '!r1', items: [item('m.text', '$1')] });
   assert.equal(