Extract y2 Ollama live-catalog default from the brand rewrite

Branch fix/y2-ollama-catalog-brand-20260901 tangles the real fix (Ollama default comes from the live local catalog: provider_defaults.rs, models.rs, model_inventory.rs, provider_lake.rs) with a mark.rs rewrite and web brand tiles that conflict with the new-logo direction. Parked, not landed. Extract the catalog-default change alone onto current main with its tests; leave brand assets to the site/mark refresh.

Compare branch fix/y2-ollama-catalog-brand-20260901 with current main, then read provider_defaults.rs, models.rs, model_inventory.rs, and provider_lake.rs to isolate the live-catalog default change. Run the existing tests for these components. Done means the Ollama default comes from the live local catalog on current main, its tests pass, and mark.rs and web brand assets remain untouched.

Written by the indexing model from the issue text.