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/split-pane-sessions-plan.md

@@ -90,6 +90,13 @@ If this asymmetry actually bothers you in daily use, promoting Pane B to full
 parity is a scoped v2 (extract the shared logic already once you have two
 call sites to compare, rather than guessing the right abstraction now).
 
+One more asymmetry worth naming here rather than discovering by surprise:
+while both panes accept keyboard input, the global capture-phase shortcut
+handler (`app.js`) always resolves against Pane A — it has no notion of
+which pane currently has focus. So Ctrl+L or Ctrl+W typed while Pane B has
+focus clears or closes Pane A, not the session you were actually typing
+into. Not fixed for v1, same reasoning as the rest of this section.
+
 ## Components
 
 ### 1. `SplitTerminalPane` (new, `terminal-split.js`)

docs/wiki/Settings-Reference.md

@@ -55,12 +55,14 @@ supervised by systemd or launchd; npm installs report as non-updatable. See
 Chips for every optional header control, with a live preview of the resulting header:
 
 Run, Font Size, System Stats, Redraw Terminal, Response Viewer, Away Digest, Session
-Manager, Attachments, File Viewer, Multi-monitor, Plan Usage, Lifecycle Log, Monitor,
+Manager, Attachments, File Viewer, Multi-monitor, Split, Plan Usage, Lifecycle Log, Monitor,
 Project Insights, File Browser, Subagents, Approvals Inbox, Read My Mind, Ultracode Agents,
 Ultracode Windows, Cron.
 
 Most default to off. The stock desktop header is system stats, File Viewer, and the gear.
-New header controls never appear on phones.
+New header controls never appear on phones. Split is desktop-only regardless of this
+setting — the button and the feature both stay off below a ~1180px viewport, where two
+resizable panes plus their divider have nowhere to go.
 
 This section also holds background-agent tracking, including whether to track agents for
 every session or only the active tab.

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.                                                              |