Transcript view (Ctrl+O) keyboard scroll keys dead in forced-fullscreen renderer (attached background/child sessions)

Follow-up to #59633 (which is resolved for normal inline sessions as of 2.1.195). A narrower case remains: when the fullscreen renderer is forced, the Ctrl+O detailed-transcript view does not respond to keyboard scroll keys.

Affected state: attached background / child sessions (e.g. claude agents / FleetView-spawned, CLAUDE_CODE_CHILD_SESSION=1). These force the fullscreen renderer — /tui reports it as forced — and CLAUDE_CODE_DISABLE_ALTERNATE_SCREEN=1 is ignored by design for them, so there is no env escape.

Repro: 2.1.195, Linux, inside tmux. Launch a child claude session (forced fullscreen, alternate_on=1), produce a long response, press Ctrl+O, try j/k and arrow keys.

Result: scroll keys do nothing. Mouse wheel only appears to work because tmux copy-mode intercepts it (not Claude scrolling).

Tried, did not help:

• CLAUDE_CODE_DISABLE_VIRTUAL_SCROLL=1 (confirmed present in the process env; keys still dead).
• CLAUDE_CODE_DISABLE_ALTERNATE_SCREEN=1 is ignored for forced-fullscreen sessions.

Originally flagged by @adtendo on #59633.