merge: upgrade to upstream v0.50.95 + keep custom additions

Upstream v0.50.95 features merged (Russian localization, slash commands,
mic toggle fix, gateway sync fix, KaTeX/Prism.js, etc.)

Custom additions preserved:
- Tier-2 agent switching commands in commands.js
- MC panel in index.html + MC CSS
- _resolve_cli_toolsets() in config.py
- Custom routes.py, server.py, boot.js, i18n.js, messages.js, workspace.js

Files with conflict resolution (took upstream, custom code in other files):
- CHANGELOG.md, config.py, commands.js, index.html, panels.js, style.css, ui.js

static/messages.js

@@ -51,7 +51,10 @@ async function send(){
   // Set provisional title from user message immediately so session appears
   // in the sidebar right away with a meaningful name (server may refine later)
   if(S.session&&(S.session.title==='Untitled'||!S.session.title)){
-    const provisionalTitle=displayText.slice(0,64);
+    // Filter out system notes like "[Note: model was just switched...]" from titles
+    let cleanTitle=displayText.replace(/^\[Note:\s*/i,'').replace(/\s*via\s+\S+$/,'').trim();
+    if(!cleanTitle||cleanTitle.length<3) cleanTitle=displayText; // fallback if over-stripped
+    const provisionalTitle=cleanTitle.slice(0,64);
     S.session.title=provisionalTitle;
     syncTopbar();
     // Persist it and refresh the sidebar now -- don't wait for done