style: UI polish and miscellaneous fixes

Fixes link color from hardcoded white to currentColor for proper theme
support. Adds video and audio modality icons to ModelInfo. Registers
anthropic, nvidia, and xiaomi in the provider icon map. Removes unused
pagination validation from agents and topics endpoints. Adds convenience
start script. Updates AGENTS.md.

app/utils/model-mapping.ts

@@ -322,7 +322,7 @@ export const providerIcons: Record<string, any | null> = {
     google: markRaw(LogoGoogle),
     openai: markRaw(LogoOpenAI),
     azure: null,
-    anthropic: null,
+    anthropic: markRaw(LogoAnthropic),
     cohere: markRaw(LogoCohere),
     huggingface: null,
     openrouter: markRaw(LogoOpenrouter),
@@ -332,6 +332,8 @@ export const providerIcons: Record<string, any | null> = {
     mistral: markRaw(LogoMistral),
     vllm: markRaw(LogoVllm),
     closedrouter: markRaw(LogoClosedRouter),
+    nvidia: markRaw(LogoNvidia),
+    xiaomi: markRaw(LogoXiaomiMiMo),
 };
 
 export function getModelConfig(modelId: string) {