feat(status): restore displays.json in diagnostics export, fix stale docs

displays.json was documented across README/troubleshooting/architecture as
part of the diagnostics ZIP but was never actually written by
collect_and_open_diagnostics_impl -- dropped in a past refactor. Restore it
using the existing geometry::win_monitor::list() enumeration plus
pick_window_rect_for_profile() to flag which monitor was auto-selected for
the active profile, so wrong-monitor/window-placement reports are
reproducible again.

Also corrects the same three docs, which all described a sidecar-parsed.json
file that doesn't exist (the real sidecar-log.txt is a plain lifecycle log,
not a parsed sensor payload) and, in architecture.md, a battery.json file
that was never exported either. Replaces an entire windows.rs module section
in architecture.md that described Tauri-era APIs (ensure_settings_window,
launch_floating_panels, panel-host.js) with no equivalent in the current
egui codebase, and fixes the README's Settings dialog size (560x600, not
560x560).

Closes #163