[Feature]: Discoverable Enter/Return-to-send preference in chat

[travelingflwr]

Problem

In my current T3 Code chat experience, sending a message requires clicking the Send button. I would like to keep my hands on the keyboard and use Return/Enter to send instead.

Requested behavior

Add a discoverable, persistent "Enter/Return sends messages" preference in chat settings:

• When enabled, Enter/Return submits the message and Shift+Enter inserts a newline.
• When disabled, Enter/Return inserts a newline and the Send button remains available.
• Show the active shortcut beside the composer or in the Send button tooltip.
• Apply the preference consistently across supported clients with physical keyboards, while retaining appropriate touch-keyboard behavior.
• Preserve IME composition and picker-selection behavior so those Enter presses do not accidentally send a message.

Context and related request

I use T3 Code Nightly on macOS and Omarchy. The exact affected build and input context have not yet been isolated; this is a request for an explicit preference and consistent keyboard behavior, rather than a claim that every desktop build lacks Enter-to-send.

Related: #8045 requests configurable submit/newline bindings, primarily to prevent accidental Enter submissions. My use case is the complementary direction: explicitly enable Enter-to-send wherever the composer currently requires clicking Send. If an existing setting already covers this, please point me to it; making it easier to discover would address the problem too.

Why this helps

Frequent conversational follow-ups should not require moving from the keyboard to the mouse for every message.

[juliusmarminge]

Resolved by #12075: there is now a discoverable Send shortcut setting (Enter by default; optional Ctrl/⌘+Enter for multiline or always). Closing this as leftover hygiene after that merge.