fix(app): make prompt submit and newline rebindable

[CasualDeveloper]

Issue for this PR

Closes #16226

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Every shortcut in the web UI is rebindable via Settings → Keyboard Shortcuts — except the one users hit most: Enter / Shift+Enter in the prompt composer. prompt-input.tsx hardcodes event.key === "Enter".

This PR registers two new web commands so they auto-surface in that settings page under the existing "Prompt" group (grouping is already driven by the prompt. id prefix in settings-keybinds.tsx):

• prompt.submit — default enter
• prompt.newline — default shift+enter

The two Enter branches in handleKeyDown now dispatch via matchKeybind(submitKeybinds(), event) / matchKeybind(newlineKeybinds(), event) against the configured bindings. event.stopPropagation() after a match so the editor always wins over the global keymap — prevents double-fire if a user picks a modified binding like mod+enter. The IME bail and the Shift+Enter-over-IME ordering are preserved.

Defaults match the previous hardcoded behavior byte-for-byte. No new config schema, no new settings UI, no migration. Same underlying ask as #11898 and #9836. (Supersedes #23378 which was auto-closed by the compliance bot for an unchecked "tested locally" box before I had run the manual walkthrough.)

How did you verify your code works?

• bun typecheck in packages/app — clean.
• bun test src/i18n/parity.test.ts src/components/prompt-input/submit.test.ts — 6 passed, 0 failed.
• Manual browser walkthrough via Chrome DevTools, driving the real composer on a built dev instance. Verified all four combinations across default and swapped bindings:

Bindings	Key pressed	Expected	Observed
Default (submit=enter, newline=shift+enter)	Shift+Enter	` ` inserted in editor	✓ `hello world` in editor innerHTML
Default	Enter (empty)	preventDefault, no submit	✓ editor untouched, zero network fetches
Swapped (submit=shift+enter, newline=enter)	Enter	` ` inserted in editor	✓ `alpha beta` in editor innerHTML
Swapped	Shift+Enter (empty)	preventDefault, no submit	✓ editor untouched, zero network fetches

• Also verified: Settings → Keyboard Shortcuts shows the new rows under the "Prompt" group; "Reset to defaults" restores `Enter` / `⇧Enter`; no accidental API submissions during any test thanks to `event.stopPropagation()` + the existing empty-content guard in `handleSubmit`.
• AI Assistance: OpenCode + anthropic/claude-opus-4-7
• Review: Human operator (@CasualDeveloper) directed the work and ran the browser walkthrough. Code inspected; behaviors verified via DOM assertions and fetch monitoring.

Screenshots / recordings

Before

After

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[Copilot]

Pull request overview

Adds rebindable keybind support for prompt submission vs newline insertion in the web prompt composer by introducing prompt.submit and prompt.newline commands and switching PromptInput’s Enter handling to keybind matching.

Changes:

• Add two new command titles to the English i18n dictionary.
• Register prompt.submit / prompt.newline commands with default bindings (Enter / Shift+Enter).
• Update PromptInput.handleKeyDown to dispatch submit/newline via matchKeybind(...) and stop propagation on matches.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/app/src/i18n/en.ts	Adds labels for the two new prompt keybind commands.
packages/app/src/components/prompt-input.tsx	Registers new commands and routes Enter handling through configured keybinds.

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