[FEATURE]: /models should keep showing all models under each provider, instead of moving recent ones into a Recents section

When opening the /models dialog in the TUI, recently used models disappear from their provider's list and are shown only in the separate "Recent" section at the top.

This is confusing: I expect the model list for a provider to be stable and complete — every model I have access to should always be listed under its provider. Right now the provider column looks "emptier" than it actually is, and I have to remember/check the Recent section to find the model I was just using. The behavior actively works against muscle memory: the same model lives in different places depending on usage history.

Proposed behavior:

• Keep all available models listed under their provider in the /models dialog, as before.
• Either remove the "Recent" section entirely, or (better, IMO) keep it as a purely additive shortcut without removing those models from their provider grouping.

Related implementation note: the sections are built in packages/tui/src/component/dialog-model.tsx (favorites + recents are currently excluded from the provider lists), so making recents additive would be a small change there.