feat(web,server): inference settings UI with per-session inference overrides

Adds Inference tab to SettingsPane with controls for temperature, top-p,
top-k, min-p, and other inference parameters. Server-side route and
provider config wiring to pass overrides through the inference pipeline.

apps/web/src/components/panes/ArenaPane.tsx

@@ -423,6 +423,7 @@ export function ArenaPane({ state, onClose }: Props) {
               duration_ms: null,
               tokens_per_sec: null,
               cost_tokens: null,
+              token_breakdown: null,
               result_path: null,
               error: null,
               created_at: new Date().toISOString(),