WiFi: Settings sub-screen with scan list, LVGL keyboard, connect flow, forget-all (#99 child 3)

[Strycher]

Epic: #99 · Parent: #99 — child 3 of 4. Plan: docs/plans/2026-09-09-wifi-configuration.md

• Status block (SSID, IP, RSSI). Scan button: async WiFi.scanNetworks into an lv_list with RSSI bars and a lock glyph.
• Tap a network: lv_textarea (masked, show/hide) + lv_keyboard (lower, upper, numbers, symbols come with the widget) -> Connect -> lv_spinner -> Connected with IP, or Failed with retry. Success saves to the store.
• Saved-network list with delete.
• Red Forget all networks button -> lv_msgbox Are you sure? with red confirm and Cancel; only the confirm wipes the store (owner, 2026-09-09).
• One-time pop-up after an SD import: Remove /config/wifi.txt? with red Remove and Keep (owner, 2026-09-09).
• The RSSI display is the usable half of Enhancement: WiFi network priority and signal strength selection #34; the rest of Enhancement: WiFi network priority and signal strength selection #34 is retired by the 5 GHz fact in the plan. Closes Enhancement: WiFi network priority and signal strength selection #34.

Acceptance: full flow on the bench with a real network; keys usable by finger; both envs build.