[FEATURE] Show active model and effort level in VS Code extension UI near the prompt input

In the VS Code extension, there's no persistent indicator of which model and effort level are currently active. The only way to check is to open the / command menu. This is disruptive mid-conversation.

The TUI has the statusLine for this, but VS Code extension users have no equivalent surface. A small label near the prompt input box (similar to how other VS Code AI extensions show model selectors) would solve this.

Suggested placement: Below or above the prompt input box, showing e.g. Opus 4.6 · max effort. Ideally clickable to open the model/effort picker directly.

Related: #41049 (effort level not in statusLine JSON — TUI), #1675 (show model below prompt — TUI, closed)

Platform: macOS, VS Code extension (not terminal TUI)