wip: context-meter + model-label UI and provider/inference tweaks

Checkpoint of in-flight work so the orchestrator branch can rebase onto a
clean main: ContextBar → ContextMeter, model-label helper, model/agent picker
+ provider-snapshot/registry changes, inference payload + message-columns.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/components/AgentPicker.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useMemo, useState } from 'react';
 import { formatAgo } from '@/lib/format';
-import { Check, ChevronDown } from 'lucide-react';
+import { Bot, Check, ChevronDown } from 'lucide-react';
 import { toast } from 'sonner';
 import { api } from '@/api/client';
 import type { Agent, AgentParseError, ToolCostStat } from '@/api/types';
@@ -90,11 +90,14 @@ export function AgentPicker({ projectId, value, onChange }: Props) {
       <DropdownMenuTrigger asChild>
         <button
           type="button"
-          className="text-xs text-muted-foreground hover:text-foreground flex items-center gap-1 px-1.5 py-0.5 rounded hover:bg-muted/60"
-          title={selectedAgent?.description ?? undefined}
+          className="inline-flex items-center gap-1.5 rounded-full border border-border px-2.5 py-1 text-xs text-muted-foreground transition-colors hover:bg-muted hover:text-foreground max-md:min-h-[36px] max-md:min-w-[36px]"
+          title={selectedAgent?.name ? `Agent: ${selectedAgent.name}` : 'No agent'}
+          aria-label={`Agent: ${triggerLabel}`}
         >
-          <span className="truncate max-w-[160px]">{triggerLabel}</span>
-          <ChevronDown className="size-3 opacity-70" />
+          <Bot className="size-3.5 shrink-0" />
+          {/* Mobile = icon only; desktop keeps the agent name + chevron. */}
+          <span className="truncate max-w-[160px] max-md:hidden">{triggerLabel}</span>
+          <ChevronDown className="size-3 opacity-70 shrink-0 max-md:hidden" />
         </button>
       </DropdownMenuTrigger>
       <DropdownMenuContent align="start" className="max-h-80 overflow-y-auto w-96">