docs(split-pane): short CLAUDE.md rule, stale module count, wiki entries, shortcut-handler caveat

CLAUDE.md previously only mentioned split-pane in the load-order list,
with nothing in the Architecture/frontend prose the way every other
feature gets, and its own module count was one stale (34, should have
been bumped to 35 when terminal-split.js was added). Add a short
pointer-style paragraph next to the other terminal features, fix the
count.

docs/wiki/The-Dashboard.md's header button table and
docs/wiki/Settings-Reference.md's header chips list are the two
user-facing surfaces that never mention Split at all; added both, plus
a note that the feature is desktop-only regardless of the setting.

docs/split-pane-sessions-plan.md: recorded the one design note that
isn't a code change — the global capture-phase shortcut handler always
resolves against Pane A, so Ctrl+L/Ctrl+W typed into Pane B affects the
other session. Not fixed for v1, same reasoning as the rest of the
"deliberately plainer" section.

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

docs/wiki/The-Dashboard.md

@@ -116,6 +116,7 @@ The right side of the header. Almost all of these are off until you enable them
 | Lifecycle Log          | Off                | Session start, exit, and kill audit trail.                                       |
 | Cron ⏰                | Off                | Scheduled jobs.                                                                   |
 | Multi-monitor          | Off, macOS         | Opens a window spanning every display.                                            |
+| Split                  | Off, desktop only  | View a second session beside the active one, with a draggable divider.           |
 | Tunnel indicator       | When a tunnel runs | Cloudflare tunnel status.                                                        |
 | Admin panel            | Multi-user only    | User administration.                                                              |