fix(ui): inline provider chip + group model count in model picker (#1425)

- Add .model-opt-provider chip (right-aligned, muted) on every model row
  that belongs to a provider group, making same-name models across
  providers visually distinguishable at a glance.
- Add per-group model count to group headings: 'OpenRouter (47)'.
- Add subtle border-top divider between provider groups for visual
  separation during scroll.

Scope: Shape A from #1425 — smallest change, ~15 LOC, no API churn.
Note: Settings model picker is a native <select> and already has optgroup
labels; this targets the custom dropdown used in the composer.

Closes #1425

static/style.css

@@ -1420,7 +1420,7 @@
 .model-dropdown{display:none;position:absolute;bottom:calc(100% + 4px);left:0;min-width:280px;max-width:min(420px,calc(100vw - 32px));background:var(--surface);border:1px solid var(--border2);border-radius:10px;box-shadow:0 -4px 24px rgba(0,0,0,.4);z-index:200;overflow:hidden;max-height:320px;overflow-y:auto;}
 .model-dropdown.open{display:block;}
 .model-scope-note{position:sticky;top:0;z-index:2;padding:9px 14px;border-bottom:1px solid var(--border);color:var(--text);font-size:11px;font-weight:650;line-height:1.4;background:color-mix(in srgb,var(--surface) 82%,var(--accent-bg));box-shadow:0 1px 0 rgba(0,0,0,.12);}
-.model-group{padding:8px 14px 4px;font-size:10px;font-weight:700;letter-spacing:.04em;color:var(--muted);text-transform:uppercase;}
+.model-group{padding:8px 14px 4px;font-size:10px;font-weight:700;letter-spacing:.04em;color:var(--muted);text-transform:uppercase;border-top:1px solid var(--border2);margin-top:2px;}
 .model-opt{padding:10px 14px;cursor:pointer;transition:background .12s;display:flex;flex-direction:column;gap:3px;align-items:flex-start;}
 .model-opt:hover{background:rgba(255,255,255,.07);}
 .model-opt.active{background:var(--accent-bg);}
@@ -1430,6 +1430,7 @@
 .model-opt-badge--primary{background:rgba(50,184,198,.16);border-color:rgba(50,184,198,.32);color:#8fe7ef;}
 .model-opt-badge--fallback{background:rgba(255,184,77,.14);border-color:rgba(255,184,77,.28);color:#ffd18a;}
 .model-opt-id{display:block;font-size:10px;color:var(--muted);line-height:1.3;opacity:.72;word-break:break-word;}
+.model-opt-provider{display:inline-flex;align-items:center;padding:1px 6px;border-radius:4px;font-size:9px;font-weight:600;letter-spacing:.03em;color:var(--muted);background:rgba(255,255,255,.05);border:1px solid var(--border2);margin-left:auto;white-space:nowrap;flex-shrink:0;}
 .model-custom-sep{padding-top:4px;border-top:1px solid var(--border);margin-top:4px;}
 .model-custom-row{display:flex;align-items:center;gap:6px;padding:6px 10px 8px;}
 .model-custom-input{flex:1;background:var(--code-bg);border:1px solid var(--border2);border-radius:6px;color:var(--text);padding:5px 8px;font-size:12px;outline:none;font-family:inherit;min-width:0;}

static/ui.js

@@ -872,19 +872,28 @@ function renderModelDropdown(){
     }
     // Add remaining models matching filter
     let _lastGroup=null;
+    // Count models per group for heading labels (#1425)
+    const _groupCounts={};
+    for(const m of _modelData){
+      if(configuredIds.has(m.value)) continue;
+      if(m.group) _groupCounts[m.group]=(_groupCounts[m.group]||0)+1;
+    }
     for(const m of _modelData){
       if(configuredIds.has(m.value)||!matches(m)) continue;
       if(m.group&&m.group!==_lastGroup){
         const heading=document.createElement('div');
         heading.className='model-group';
-        heading.textContent=m.group;
+        const count=_groupCounts[m.group]||0;
+        heading.textContent=count>1?`${m.group} (${count})`:m.group;
         dd.appendChild(heading);
         _lastGroup=m.group;
       }
       const row=document.createElement('div');
       row.className='model-opt'+(m.value===sel.value?' active':'');
       const badgeHtml=m.badge?`<span class="model-opt-badge model-opt-badge--${esc(m.badge.role||'configured')}">${esc(m.badge.label||'Configured')}</span>`:'';
-      row.innerHTML=`<div class="model-opt-top"><span class="model-opt-name">${m.name}</span>${badgeHtml}</div><span class="model-opt-id">${m.id}</span>`;
+      // Inline provider chip on every row that has a group (#1425)
+      const providerChip=m.group?`<span class="model-opt-provider">${esc(m.group)}</span>`:'';
+      row.innerHTML=`<div class="model-opt-top"><span class="model-opt-name">${m.name}</span>${badgeHtml}${providerChip}</div><span class="model-opt-id">${m.id}</span>`;
       row.onclick=()=>selectModelFromDropdown(m.value);
       dd.appendChild(row);
     }