[web] Send button overlaps the model reasoning/thinking-depth selector on mobile (iPhone), blocking Send and Stop

Description

On the opencode web UI opened from an iPhone browser, the Send button overlaps the model reasoning-depth (thinking) selector button. The overlap happens at all screen sizes (not only when the window is narrow), so the Send button and, while a response is streaming, the Stop button can no longer be tapped. The only workaround is to use the on-screen keyboard's Return key to submit.

Environment

• opencode version: 1.18.14
• Interface: opencode web (opencode web), opened in a mobile browser
• Client: iPhone (mobile Safari; reproduces regardless of iPhone model, so this looks like a general mobile layout issue)
• Host: Linux (Ubuntu, kernel 6.8.0-139-generic)

Steps to reproduce

1. Start opencode web and open it in a browser on an iPhone.
2. Open a session so the prompt input and the model / reasoning-depth selector are visible.
3. Observe the bottom-right area of the input bar.

Expected

The Send button and the reasoning-depth selector are laid out without overlapping, and both remain tappable on mobile viewports.

Actual

• The two controls overlap. The Send button (and the Stop button while streaming) is covered / not reliably tappable.
• Tapping in that area toggles the model/thinking selector instead of sending/stopping.

Impact

High: on iPhone, sending a message or stopping generation is impossible via touch; users must fall back to the Return key, and there is no touch way to stop a long response.

Additional context

• Confirmed still present as of 1.18.14.
• Reproduces on any iPhone model, so it is likely a responsive-layout bug in the prompt input toolbar (controls not wrapping / absolutely positioned on top of each other at small widths).

Start by locating the web prompt input toolbar and reproducing the issue in an iPhone or mobile viewport. Inspect the layout of the Send/Stop control and model reasoning-depth selector; done means both controls remain separate and tappable while sending and streaming.