fix(remote): keep the remote screen rows above the local frame in a remote history load

The remote history and the local frame are read a round trip apart, so
two seams dropped rows at the join: rows that scrolled off the screen
during the round trip, and the top of a remote screen taller than this
pane (a shared session sized by a taller client under window-size
latest). Both are rows of the remote screen above where the local frame
begins.

The remote script now also captures the screen, right after the
history, in the same round trip. joinScrollbackAndFrame() places the
local frame among the screen rows (findFrameInScreen(): text compare
with escape sequences and trailing blanks ignored, the screen's trailing
blank rows and last content row left out, at least three rows of
overlap with two of them non-blank, highest match wins) and keeps the
screen rows above it between the history and the frame. When the frame
cannot be placed, the join is history over frame as before. The read's
buffer slack grows to 1 MiB, since the screen is outside the tail -c
bound.

Left: the history and screen are two tmux commands, so a row that
scrolls between them (milliseconds) is lost, and a screen that repeats
a whole block can place the frame at the higher copy, losing the rows
between the copies.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/web/routes/session-routes.ts

@@ -3128,7 +3128,10 @@ export function registerSessionRoutes(
         captureOpts.historyLimitLines,
         terminalBufferMaxBytes
       );
-      if (remoteScrollback !== null) captureOpts.scrollbackOverride = remoteScrollback;
+      if (remoteScrollback !== null) {
+        captureOpts.scrollbackOverride = remoteScrollback.scrollback;
+        captureOpts.scrollbackOverrideScreen = remoteScrollback.screen;
+      }
     }
     const liveMuxBuffer =
       muxName && typeof ctx.mux.captureActivePaneBuffer === 'function'