feat(mobile): long-press to select terminal text, tap to extend, Copy

There was no way to copy terminal text from a phone at all, and three layers
ruled it out independently: `user-select: none` across the whole terminal subtree
on touch devices (taps are cursor gestures there, so the OS callout had to go),
the WebGL renderer drawing glyphs as pixels with only the accessibility tree
behind them, and xterm's own selection being a mouse DRAG while the touch path
dispatches a zero-movement mousedown/mouseup pair — a click. `copyTerminal()`
exists but is wired to no button and calls `navigator.clipboard` directly, which
is undefined on the plain-HTTP LAN install the installer offers.

So the gesture drives xterm's `select()` directly: public API, renderer-
independent, and the highlight is drawn by xterm itself. Long-press is free real
estate — tap and swipe are taken, long-press and double-tap are used by nothing.

- **Long-press** (350ms, finger still within the shared tap slop) selects the
  run of non-whitespace under the finger. Whitespace is the only delimiter on
  purpose: every punctuation-aware word rule cuts a path, URL or hash in half,
  which is what you came to copy.
- **Drag** while held extends the selection; touchmove diverts from scrolling.
- **Tap** while the bar is up extends it too. That is the ergonomic core:
  picking up a 4px handle with a fingertip is a coin flip, tapping the other end
  is not. Dismissal stays explicit (✕ or Copy), so no tap is spent leaving a mode
  the user is still using.
- **Copy** goes through the existing `copyTerminalSelection()`, so it inherits
  the execCommand fallback that is the only route that works on plain HTTP.
- **Line** takes the whole logical line, wraps included, trailing pad trimmed.

Three guards are what make the gesture survive contact with a real phone, and
each fixes a symptom measured on Android Chrome:

1. **The compat mouse pair after touchend.** xterm focuses from its screen-element
   mousedown and SelectionService resets the model there, so lifting your finger
   popped the keyboard and dissolved the selection in one go. The tap path already
   had a guard for those events; the selection path simply never armed it. Armed
   now, and the touchend is `preventDefault`ed so the synthesis is stopped at the
   source (that listener is no longer passive).
2. **The platform's own long-press.** Android Chrome runs its handling at ~500ms
   and focuses the nearest editable element — xterm's helper textarea, parked at
   the cursor — which no touch handler can preventDefault because it never sees an
   event. A focus guard blurs the terminal input for the duration of the gesture,
   whatever focused it, bounded by a self-expiring deadline so a stuck flag can
   never leave the keyboard unreachable. `contextmenu` is suppressed for the same
   window, and the threshold sits at 350ms so it lands clear of the platform's.
3. **Copy re-focusing the terminal.** `copyTerminalSelection()` ends with
   `terminal.focus()`, which is right on a desktop and wrong on a phone: the
   keyboard covers what was just copied with nothing waiting to be typed.

The bar is built in JS because index.html is read once at server start, and its
styles live in styles.css rather than mobile.css because the gesture is
touch-driven, not width-driven — a touch tablet in landscape gets the gesture and
would otherwise have no bar to copy from.

12 tests in `terminal-touch-tap.test.ts` cover the word rule, forward and
backward extension, cross-row selection, Line, tap-to-extend, the copy path, and
each of the three guards including the focus guard's expiry.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/web/public/styles.css

@@ -3395,6 +3395,57 @@ body.touch-device .terminal-container .xterm .xterm-helper-textarea {
   -webkit-touch-callout: none !important;
 }
 
+/* Touch text-selection bar (long-press → select → Copy).
+   Lives in styles.css, NOT mobile.css: the gesture is touch-driven, not
+   width-driven, and mobile.css is media-gated to ≤1023px — a touch tablet in
+   landscape would get the gesture with no bar to copy from.
+   Built in JS (index.html is read once at server start, so markup added there
+   would need a restart to appear). z-index 900 sits above terminal content and
+   the local-echo overlay (7) and deliberately BELOW floating agent windows
+   (1000), so it can never cover their controls. */
+.term-select-bar {
+  position: absolute;
+  z-index: 900;
+  display: none;
+  gap: 2px;
+  padding: 3px;
+  background: var(--bg-card);
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  box-shadow: 0 4px 14px rgba(0, 0, 0, 0.45);
+}
+
+.term-select-bar.visible {
+  display: flex;
+}
+
+.term-select-btn {
+  min-height: 38px;
+  min-width: 46px;
+  padding: 0 0.7rem;
+  border: none;
+  border-radius: 6px;
+  background: transparent;
+  color: var(--text);
+  font-family: inherit;
+  font-size: 0.82rem;
+  font-weight: 600;
+  cursor: pointer;
+  /* The bar is the one place in the terminal subtree a tap must land on a
+     control rather than a cell, so it opts out of the gesture styles above. */
+  touch-action: manipulation;
+}
+
+.term-select-btn:active {
+  background: var(--bg-hover);
+}
+
+.term-select-btn--close {
+  min-width: 38px;
+  padding: 0;
+  color: var(--text-muted);
+}
+
 /* Welcome Overlay */
 .welcome-overlay {
   position: absolute;