Feature request: emit a distinct CSI-u sequence for Ctrl+Enter in terminal blocks

从 frontend/app/view/term/term-model.ts 中的 handleTerminalKeydown() 开始，将现有的 Shift+Enter 处理与所请求的 Ctrl+Enter 情况进行比较。验证 Enter、Shift+Enter、Ctrl+Enter 和 Alt+Enter 的原始字节，确认现有的 Enter 行为保持不变，并确认新序列在所述平台上都能正常工作。

Feature description

Please add terminal-block handling for Ctrl+Enter so WaveTerm emits a distinct key sequence instead of collapsing it to the same byte as Enter/newline.

A practical default would be to send the CSI-u representation for Ctrl+Enter:

ESC [ 13 ; 5 u

or, as a JavaScript string:

"\x1b[13;5u"

This would let terminal applications distinguish Ctrl+Enter from plain Enter and Shift+Enter.

Why this matters

Many interactive terminal applications and coding/chat CLIs support configurable input behavior such as:

• Enter inserts a newline
• Ctrl+Enter submits/sends the message

This is useful for multi-line prompts in AI/coding tools and other REPL-like terminal UIs.

Today, WaveTerm can already special-case modified Enter keys. PR #2523 added related handling for Shift+Enter newline support in frontend/app/view/term/term-model.ts. This request is the analogous missing case for Ctrl+Enter.

Current behavior

Testing in WaveTerm with a raw byte reader shows:

Enter        -> 0a
Shift+Enter  -> 0a
Ctrl+Enter   -> 0a
Alt+Enter    -> 1b 0a

So Enter, Shift+Enter, and Ctrl+Enter are indistinguishable to the program running inside the terminal. Alt+Enter is distinguishable because it carries an ESC prefix.

Expected behavior

Ctrl+Enter should produce a distinct sequence, for example:

Ctrl+Enter -> 1b 5b 31 33 3b 35 75

which is:

\x1b[13;5u

Terminal applications that understand CSI-u can then bind ctrl+enter separately from enter.

Suggested implementation

In frontend/app/view/term/term-model.ts, inside handleTerminalKeydown(), add a Ctrl:Enter branch near the existing Shift:Enter branch:

if (keyutil.checkKeyPressed(waveEvent, "Ctrl:Enter")) {
    this.sendDataToController("\x1b[13;5u");
    event.preventDefault();
    event.stopPropagation();
    return false;
}

This mirrors the existing approach used for Shift:Enter, but sends a standard CSI-u modified-key sequence instead of a newline byte.

Validation

After applying this locally, the raw-byte test becomes:

Enter        -> 0a
Shift+Enter  -> 0a
Ctrl+Enter   -> 1b 5b 31 33 3b 35 75
Alt+Enter    -> 1b 0a

With that output, applications such as Pi can configure:

{
  "tui.input.newLine": ["enter", "shift+enter", "ctrl+j"],
  "tui.input.submit": ["ctrl+enter"]
}

and get the intended behavior without local WaveTerm binary patching.

Related work

• #2523 added terminal input improvements, including Shift+Enter newline support.
• This request extends the same terminal-block keydown handling pattern to Ctrl+Enter.

Acceptance criteria

• Ctrl+Enter in a terminal block emits \x1b[13;5u or another documented distinct Ctrl+Enter sequence.
• Enter and Shift+Enter behavior remains unchanged.
• The behavior works on Linux, macOS, and Windows where the browser/Electron key event exposes Ctrl+Enter.
• The behavior is documented if WaveTerm has terminal key handling documentation.