Stop the terminal's Enter key dismissing the keyboard it was typed on

The first device run of ADR 0015 found the premise held and the field misconfigured
in a second way: the suggestion strip, autocorrect and predictive text were all
gone, and every Enter closed the keyboard. On a terminal that is every command, so
the phone asked for a tap between each one.

TerminalInputSurface had been left with Avalonia's default ReturnKeyType, and the
same OnCreateInputConnection that carries the inputType fix maps that default, on a
field that is not Multiline, to IME_ACTION_DONE:

    _ => options.Multiline ? 1073741824 : 6,   // 6 is IME_ACTION_DONE

Done means done. The keyboard performs the action and dismisses itself, which is
right for the text box the default was written for and wrong for a surface where
Enter is punctuation rather than submission.

TextInputReturnKeyType.Return is the member that maps to IME_ACTION_NONE — value 1,
so `returnKeyType - 1 => 0 => 1073741824` — leaving Enter a plain newline with no
action attached and no reason for the IME to hide.

◆ THE TRAP, WHICH IS THE ONE 11.10b ALREADY WARNED ABOUT FROM THE OTHER SIDE.

Multiline=true also reaches IME_ACTION_NONE, through that same default arm, and is
the obvious fix and the wrong one. It ORs TYPE_TEXT_FLAG_MULTI_LINE into InputType,
which moves it off 1 and silently fails the ShowSuggestions guard the whole ADR
turns on. Taking the obvious route to a working Enter would have handed the
suggestion strip back and looked like the premise had failed rather than like the
fix had. ReturnKeyType touches imeOptions only, which is why it is what is set.

Enter's byte was never the problem and is not what changed: IME_ACTION_DONE was
already synthesising KEYCODE_ENTER through AvaloniaInputConnection.PerformEditorAction,
so commands did run — the keyboard just left afterwards.

OnTextInput now also normalises line endings to CR. Belt and braces for the case
this change makes newly possible: a keyboard with no editor action attached may
commit "\n" as ordinary text rather than sending KEYCODE_ENTER, and a shell handed
LF for Enter looks like a shell that ignored the key. Normalising rather than
special-casing also stops a pasted "\r\n" running its line twice.

Check 11.10e is the regression test, and says in as many words not to fix a
recurrence with Multiline.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/adr/0015-android-terminal-input.md

@@ -84,6 +84,7 @@ and keeps it for as long as that surface is up.
 
 - `TextInputOptions.ShowSuggestions = false`, with `ContentType`, `Multiline` and `AutoCapitalization`
   left at the defaults the guard above requires. This is the entire fix for the suggestion strip.
+- `TextInputOptions.ReturnKeyType = Return`, which is the fix for Enter — see the correction below.
 - It implements `TextInputMethodClient` with an empty surrounding text and a zero-length selection.
   A terminal has no document for an IME to edit; committed text is forwarded and nothing is retained.
 - Committed text and key events are encoded to bytes and written to the session through the same path
@@ -144,9 +145,35 @@ software keyboard. It never did before — everything typed went straight into t
 `SendAsync`, which is where the latch lives — so `ctrl` then `c` was inert unless the second key also came
 from the accessory row. Check 11.10d covers it.
 
-**Verify before building anything on this:** checks 11.10a–11.10d in `docs/manual-checks.md`, and 11.10b
+**Verify before building anything on this:** checks 11.10a–11.10e in `docs/manual-checks.md`, and 11.10b
 first of all, because it is the falsification test at the end of this document.
 
+> **⚠️ Corrected on the first device run: every Enter closed the keyboard.** The premise held — the
+> suggestion strip, autocorrect and predictive text were all gone — but the field had been left with
+> Avalonia's default `ReturnKeyType`, and the same `OnCreateInputConnection` maps that, on a field that is
+> not `Multiline`, to `IME_ACTION_DONE`:
+>
+> ```csharp
+> _ => options.Multiline ? 1073741824 : 6,   // 6 is IME_ACTION_DONE
+> ```
+>
+> Done means done: the keyboard performs the action and dismisses itself. On a text box that is right, and
+> on a terminal it fires on every command. `TextInputReturnKeyType.Return` — value 1, so
+> `returnKeyType - 1 => 0 => 1073741824` — is `IME_ACTION_NONE`, which leaves Enter a plain newline with no
+> action for the IME to perform and no reason for it to hide.
+>
+> **The trap worth recording, because it is the same trap 11.10b already warned about from the other side:**
+> `Multiline = true` also reaches `IME_ACTION_NONE`, through the default arm, and is the wrong way there. It
+> ORs `TYPE_TEXT_FLAG_MULTI_LINE` into `InputType`, which moves it off `1` and silently fails the
+> `ShowSuggestions` guard. Taking the obvious route to a working Enter would have handed the suggestion
+> strip back and looked like the whole ADR had failed. `ReturnKeyType` touches `imeOptions` only.
+>
+> Enter's *byte* was never in doubt and is not what changed — `IME_ACTION_DONE` was already synthesising
+> `KEYCODE_ENTER` through `AvaloniaInputConnection.PerformEditorAction`, so commands ran; the keyboard just
+> left afterwards. `OnTextInput` now also normalises line endings to CR, for the case where a keyboard with
+> no editor action commits `"\n"` as ordinary text instead of sending a key event, and so that a pasted
+> `"\r\n"` does not run its line twice.
+
 ### Stage 2 — the keys around it
 
 Only once Stage 1 is proven, because each of these is cheap *given* Avalonia owning input and awkward