feat(ui): chat frontend, model picker, streaming, admin, a11y

Preview/UI work: chat renderer, streaming/think-trace, model picker
(instant-open/refresh-backoff), admin panel, a11y, gallery landing.

Source: vendor/photocraft (ad1cff44) static files, 3-way merged onto
upstream/dev (a8c147b2). Resolution policy in pr_work/D_conflicts.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

static/js/research/jobs.js

@@ -80,7 +80,10 @@ export function init(apiBase) {
   // sidebar — _reconnectActive only ran once at load before, so
   // agent-started jobs never appeared until a page reload.
   if (_activePollInterval) clearInterval(_activePollInterval);
-  _activePollInterval = setInterval(() => { _reconnectActive(); }, 20000);
+  _activePollInterval = setInterval(() => {
+    if (document.hidden) return;
+    _reconnectActive();
+  }, 60000);
 }
 
 // Allow an immediate adopt when the chat stream signals a new research