feat: add model dropdown with provider logos and tier badges

- Create model catalog (src/shared/domain/models.ts) with 12 models
  from OpenAI, Anthropic, and Google including tier metadata
- Replace free-text model input with custom ModelSelect dropdown
  grouped by provider with colored provider icons (green AI for
  OpenAI, orange A for Anthropic, blue G for Google)
- Show tier badges (premium/standard/fast) on each model option
- Highlight currently selected model with indigo accent
- Update ActivityPanel to show provider icons on model badges
  for visual consistency across the app

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/renderer/components/ActivityPanel.tsx

@@ -1,5 +1,5 @@
 import { useMemo } from 'react';
-import { Activity, Bot, Cpu, Sparkles } from 'lucide-react';
+import { Activity, Bot, Sparkles } from 'lucide-react';
 
 import {
   buildAgentActivityRows,
@@ -8,9 +8,16 @@ import {
   isAgentActivityCompleted,
   type SessionActivityState,
 } from '@renderer/lib/sessionActivity';
+import { inferProvider, type ModelProvider } from '@shared/domain/models';
 import type { PatternDefinition } from '@shared/domain/pattern';
 import type { SessionRecord } from '@shared/domain/session';
 
+const providerStyles: Record<ModelProvider, { bg: string; text: string; label: string }> = {
+  openai: { bg: 'bg-emerald-500/15', text: 'text-emerald-400', label: 'AI' },
+  anthropic: { bg: 'bg-orange-500/15', text: 'text-orange-400', label: 'A' },
+  google: { bg: 'bg-blue-500/15', text: 'text-blue-400', label: 'G' },
+};
+
 function formatModel(model: string): string {
   return model.replace(/-/g, '\u2011');
 }
@@ -92,7 +99,18 @@ export function ActivityPanel({ activity, pattern, session }: ActivityPanelProps
                 {agent && (
                   <div className="mt-1.5 flex flex-wrap items-center gap-1.5">
                     <span className="inline-flex items-center gap-1 rounded bg-zinc-800 px-1.5 py-0.5 text-[10px] font-medium text-zinc-400">
-                      <Cpu className="size-2.5" />
+                      {(() => {
+                        const prov = inferProvider(agent.model);
+                        if (prov) {
+                          const s = providerStyles[prov];
+                          return (
+                            <span className={`flex size-3.5 items-center justify-center rounded text-[7px] font-bold ${s.bg} ${s.text}`}>
+                              {s.label}
+                            </span>
+                          );
+                        }
+                        return null;
+                      })()}
                       {formatModel(agent.model)}
                     </span>
                     {agent.reasoningEffort && (