[FEATURE]: Make the model and variant labels in the TUI prompt footer clickable

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Make the model and variant (reasoning effort) labels in the TUI prompt footer clickable.

In the prompt footer (Build · DeepSeek V4.1 Flash DeepSeek · high), the variant label (high) is display-only. Today the only ways to change it are ctrl+t (variant_cycle) or binding variant_list, which has no default key. Mouse users have no way to change the variant, and new users don't find out that it can be changed at all.

Proposal

• Single click on the variant label → cycle to the next variant (same as variant_cycle / ctrl+t).
• Double click on the variant label → open the variant picker dialog (same as variant_list).

Implementation note

A terminal double click arrives as two separate clicks, so a naive implementation would cycle twice and then open the list. The single-click action would have to be deferred for a short window (~300 ms) until it's clear no second click is coming. If that delay feels too laggy, this alternative avoids the conflict:

• Left click → cycle the variant
• Right click (or shift+click) → open the variant list

The change looks small. In packages/tui/src/component/prompt/index.tsx, the variant <text> inside <Show when={showVariant()}> could get an onMouseUp handler that dispatches the existing commands, e.g. keymap.dispatchCommand("variant.list"). Both commands already exist, so no new logic is needed.

Model name

• Click on the current model name → open the model picker (same as model_list / <leader>m).

This uses the existing model.list command, so it's the same one-line onMouseUp change on the model <text> in the same component.