fix(terminal): drive the shipped Shift+Enter handlers and the Key tester cap in their browser tests (#520, #522 review)

- Minor: the Key tester "14 lines" test never pressed a key into the
  tester (the previous test blurred it, so the presses landed on <body>
  and the cap was never exercised). It now refocuses the field, asserts
  the focus, clears the log, checks 2 presses accumulate to 6 lines, then
  4 presses of another key cap the log at exactly 14 with the oldest 4
  lines evicted in order, and the readonly field stays empty. Verified to
  fail with the cap changed to 20.
- Nit: the split-pane invariant implied Ctrl+Enter could use the CLI's
  declared newline chord. Reworded after checking the send-key route:
  Ctrl+Enter is always a real 0x0a, Shift+Enter is the declared
  capabilities.newline chord (0x0a unless the CLI declares another), sent
  on keydown only. The same imprecision in the auto-named sessions
  paragraph is corrected too.
- Nit: docs/wiki/Settings-Reference.md now lists the Key tester row in
  the Terminal & Input table.

- Nit: test/shift-enter-keypress.browser.test.ts exercised a hand-copied
  predicate named `shipped`. It now loads the real app from a real
  WebServer and presses real keys into the handlers terminal-ui.js
  (app.terminal, recording the real _sendInputAsync send path) and
  terminal-split.js (a real SplitTerminalPane) attach, recording the
  send-key POSTs through a fetch wrapper. It asserts no \r reaches either
  send path for Shift/Ctrl+Enter, exactly one send-key per press for the
  right session, and that Enter and Alt+Enter are untouched. The old
  keydown-only gate stays as a labelled reproduction of xterm's keypress
  behaviour on a bare Terminal. Verified to fail on both panes with the
  gate narrowed back to keydown.
- Nit: the keypress trap is now written down beside the other key-gate
  rules (Command palette and shortcut registry): xterm runs the custom
  handler for keydown, keypress and keyup and drops only Ctrl/Alt/Meta
  keypresses, so a gate on a chord that can carry Shift alone must
  swallow every event type. The smart-copy keydown-only rule points at it.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/wiki/Settings-Reference.md

@@ -50,6 +50,7 @@ supervised by systemd or launchd; npm installs report as non-updatable. See
 | Normal / Bold font weight     | xterm defaults       | Per device, each slot from 100 to 900. The bundled JetBrains Mono renders every step, so a lighter normal weight makes Claude's bold headings stand out. Applies live to the terminal, both echo overlays and open team panes. |
 | WebGL Renderer                | On                   | With a GPU-stall watchdog that falls back to DOM rendering.            |
 | Gesture Control               | Off                  | Camera hand tracking. Also needs `CODEMAN_GESTURE=1` on the server.    |
+| Key tester                    | n/a                  | A diagnostic that stores nothing. Click the box and press keys to see what this browser reports (key, code, modifiers) for keydown, keypress and keyup, for when a chord such as Shift+Enter behaves differently on one device. Keys pressed there reach no session and trigger no shortcut. |
 
 ### Header & Panels