Add find-in-scrollback, unicode11, and keyboard pane navigation

Three xterm.js features, implemented together because they share the
XtermPane mount + the single attachCustomKeyEventHandler:

- Unicode 11: load @xterm/addon-unicode11, set activeVersion='11' after
  the canvas renderer so emoji/CJK/box-drawing widths stop drifting.
- Find in scrollback: @xterm/addon-search + a new per-pane SearchBar
  overlay (Ctrl+Shift+F to open, Enter/Shift+Enter next/prev, regex +
  case toggles, Esc to close & refocus). Overlay is an absolutely-
  positioned sibling in a position:relative wrapper so fit() is unaffected.
- Pane navigation: Ctrl+Alt+Arrow / Ctrl+Alt+HJKL (spatial neighbour via
  findNeighborInDirection) and Alt+1..9 (Nth leaf in walkLeaves order).
  XtermPane emits a NavigateIntent; App resolves the target leaf and sets
  it active, reusing the existing isActive->focusTrigger refocus chain.

All chords live in one attachCustomKeyEventHandler (xterm replaces the
handler on each call). Shortcuts added to shortcuts.ts (SoT for README +
Help), including the Alt+digit shell-conflict caveat. tsc clean apart
from the three not-yet-installed addon modules.

Needs pnpm install on the Windows host + runtime verification.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/shortcuts.ts

@@ -66,7 +66,23 @@ export const SHORTCUT_SECTIONS: ShortcutSection[] = [
       { keys: "Ctrl+K", description: "Open jump-to-pane palette" },
       {
         keys: "Ctrl+Shift+← / → / ↑ / ↓",
-        description: "Focus neighbour pane in that direction",
+        description:
+          "Focus neighbour pane in that direction (window-level — works even when no terminal is focused)",
+      },
+      {
+        keys: "Ctrl+Alt+← / → / ↑ / ↓",
+        description:
+          "Focus neighbour pane in that direction (from inside the terminal — intercepted before the PTY sees it)",
+      },
+      {
+        keys: "Ctrl+Alt+H / J / K / L",
+        description:
+          "Same as Ctrl+Alt+Arrow but in Vim-style HJKL order (left / down / up / right)",
+      },
+      {
+        keys: "Alt+1 … Alt+9",
+        description:
+          "Focus the Nth pane in layout order (DFS: left-to-right, top-to-bottom); clamped to pane count. Note: swallows bare Alt+digit — shells using readline digit-argument or vim buffer-jump may conflict.",
       },
     ],
   },
@@ -100,6 +116,18 @@ export const SHORTCUT_SECTIONS: ShortcutSection[] = [
         keys: "Ctrl+Shift+C / Ctrl+Shift+V",
         description: "Copy selection / paste in terminal",
       },
+      {
+        keys: "Ctrl+Shift+F",
+        description: "Open find-in-scrollback bar for the focused pane",
+      },
+      {
+        keys: "Enter / Shift+Enter",
+        description: "Next / previous match (while search bar is focused)",
+      },
+      {
+        keys: "Escape",
+        description: "Close find bar and return focus to terminal",
+      },
     ],
   },
   {