fix(ui): clear session search on boot + autocomplete=off + pageshow bfcache handler (closes #822)

* fix(ui): clear session search on boot + autocomplete=off — prevents bfcache from restoring stale filter (closes #822)

* fix(ui): add pageshow handler for true bfcache restore case (#822 completion)

The original PR's two fixes cover fresh page loads and hard reloads —
but the bug the issue describes happens on *bfcache restore* (Chrome's
back-forward cache).  The async boot IIFE does NOT re-run when the
browser restores a page from bfcache; the DOM is restored in place,
including any stale #sessionSearch value.  The boot-time clear has no
effect there.

`autocomplete="off"` is a hint that Chrome and others sometimes honour
for bfcache but is not reliable for user-typed values (as opposed to
autofill candidates).

Add a pageshow event listener that checks event.persisted === true and,
on that path only, clears #sessionSearch and re-renders from cache.
Fresh loads skip the listener (persisted=false) and continue to be
handled by the boot IIFE.

Also added tests/test_session_search_bfcache_822.py with 7 tests:
- autocomplete="off" present on the input
- boot-time clear runs before the first renderSessionList
- pageshow listener registered
- handler guards on event.persisted
- handler clears the search field and triggers a re-render

Full suite: 1745 passed, 0 failures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: nesquena-hermes <nesquena-hermes@users.noreply.github.com>
Co-authored-by: Nathan Esquenazi <nesquena@gmail.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

static/index.html

@@ -40,7 +40,7 @@
           <span data-i18n="new_conversation">New conversation</span> <span style="font-size:10px;opacity:.5;margin-left:4px">Cmd+K</span>
         </button>
       </div>
-      <div class="session-search"><input id="sessionSearch" placeholder="Filter conversations..." data-i18n-placeholder="filter_conversations" oninput="filterSessions()"></div>
+      <div class="session-search"><input id="sessionSearch" placeholder="Filter conversations..." data-i18n-placeholder="filter_conversations" oninput="filterSessions()" autocomplete="off"></div>
       <div class="session-list" id="sessionList"></div>
     </div>
     <!-- Tasks (cron) panel -->