Follow herdr focus: do not take the view while typing or in a dialog (#1432 follow-ups) #1470

Follow-ups from the merge pass's review of #1432 (omo-native-code-reviewer; traced in code, not reproduced).

MEDIUM: following takes the view away mid-interaction. Nothing checks for a focused composer or terminal, an unsent draft, a prompt card, or an open Files dialog or file viewer (src/App.tsx around 732-740, src/lib/followFocus.ts around 20-22). A phone with the setting on that is typing in pane A's composer jumps to pane B when someone clicks B in herdr's window; the keyboard drops and an open file viewer closes. Nothing is lost or misrouted (drafts are per pane, the hidden pane gives up keyboard focus). Skip following while this device's input has focus, a draft is unsent or a dialog covers the pane, or say so in DESIGN.md.

LOW

• With the setting on, this device's own "split and focus" can lose its keyboard focus when the follow frame arrives before the split's answer (the new pane is opened as an automatic pick, so the input is not raised and no Back entry is added).
• scripts/follow-focus-regression.ts: if it fails partway the setting stays on (finally closes the tabs but does not turn the toggle off).
• With a remote PC whose bridge is older, the setting silently does nothing for that PC; its description does not say so.