Diagnostics sub-screen: show WiFi status and IP; make the page scroll (#99 gap)

[Strycher]

Epic: #99 · Parent: #99 — gap filed by the owner 2026-09-09 after the first #295 boot on the bench.

The Settings > Diagnostics sub-screen (screen_settings.cpp, sub-screen 4, 11 fixed rows at 21 px) has a Web: row but nothing a user can read as WiFi status, and the container is created with LV_OBJ_FLAG_SCROLLABLE cleared, so there is no room for more rows on the 320 px panel.

• WiFi row: state (connecting / connected / waiting / no networks, from the WiFi: NVS credential store, non-blocking connect, one-shot SD import (#99 child 1) #295 state machine), SSID, IP and RSSI when connected.
• The rows live in a vertically scrollable container so more diagnostics can be added; keep the existing 11 rows and their live updates.
• Touch scroll and the button scroll used elsewhere in Settings.

Acceptance: WiFi row reads correctly through boot, connect and loss on the bench; page scrolls; both envs build.