feat(ui-lvgl): on-device map download over WiFi

The map's download button fetches the visible area (overview levels up to
a chosen zoom) into /sdcard/maps from OpenTopoMap or maps/source.txt,
skipping tiles already on the card and rejecting placeholder answers.
Settings > WiFi stores the network in NVS (with scan); WiFi is on only
while a download runs. HTTP runs on a worker task on core 0; the popup
shows link, internal heap and the last TLS/HTTP error.

Internal RAM was the blocker (~13 KB free with WiFi + Bluedroid): the L2
LVGL env now allocates the_mesh in PSRAM (MESH_IN_PSRAM, static RAM
210 -> 87 KB) and mbedTLS allocates from PSRAM. Confirmed on hardware.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/development/ui-core.md

@@ -147,7 +147,7 @@ consumes keys only.
 - Theme tokens (colours, spacing, typography) in one place — the first chance to realise the "Amber Trace" direction in colour.
 - Fonts ✅ Noto Sans generated by `ui-lvgl/fonts/generate.sh` (lv_font_conv): European Latin (Latin-1, Extended-A/B), Greek, Cyrillic + supplement, typographic punctuation, currency, LVGL symbols; 12/14/16/20 px, clock 40 px digits only. On-screen keyboard (`ui-lvgl/Keyboard.h`), phone-style: one layout per script (Latin QWERTY / Cyrillic ЙЦУКЕН / Greek) chosen by the same `keyboard_main_alphabet` / `keyboard_alt_alphabet` prefs as `ui-new` (globe key switches), hold a key for its variants; compose limit counted in UTF-8 bytes. Long-press variants and UTF-8 case mapping are shared with `ui-new` in `ui-core/KeyboardData.h`.
 - Simulator ✅: `SIM_UI=lvgl variants/sim/build_wasm.sh` builds the same `ui-lvgl` code for the browser (`SimLcdDisplay` in `variants/sim/SimDisplayDriver.h` blits LVGL's RGB565 flush to a 320×240 canvas; the `SIM_PLATFORM` branch of `ui-lvgl/LvglPort.h` feeds the mouse in as touch). LVGL comes from the L2 env's PlatformIO libdeps; its objects are cached in `web/build/obj_lvgl/`. `web/lvgl.html` runs it next to a `ui-new` peer on a direct link (buttons: advert, peer DM, peer → Public, the board button) and exposes `window.sim` (`tap`, `hold`, `touch`, `peerDM`, `peerChannel`) for headless checks.
-- Map (in progress): offline Web-Mercator raster tiles on the microSD (`/maps/{z}/{x}/{y}.png`, the Meshtastic MUI layout; optional per-column `.pak` from PR #3381's packer), SDMMC 1-bit mount in `LvglPort.h`. `ui-lvgl/map/TileProvider.h` is the swap point: the screen and `map/TileCache.h` (12 decoded RGB565 tiles in PSRAM, LRU) only call `renderTile(z, x, y, rgb565)`, so a vector renderer can replace the PNG provider later. `MapScreen.h`: pan by drag, +/-, re-centre/follow GPS, Nearby nodes with a position as markers (tap = node detail), one tile decoded per loop pass. `maps/attribution.txt` is shown on the map. Planned split (user, 2026-09-25): a Nodes map (every contact with a position) and a separate Navigation map (waypoints + live shares only, for walking to a target). Tiles come from `tools/maps/fetch_tiles.py` (no default server: tile.openstreetmap.org blocks offline use) or, next, an on-device WiFi download of the visible area.
+- Map (in progress): offline Web-Mercator raster tiles on the microSD (`/maps/{z}/{x}/{y}.png`, the Meshtastic MUI layout; optional per-column `.pak` from PR #3381's packer), SDMMC 1-bit mount in `LvglPort.h`. `ui-lvgl/map/TileProvider.h` is the swap point: the screen and `map/TileCache.h` (12 decoded RGB565 tiles in PSRAM, LRU) only call `renderTile(z, x, y, rgb565)`, so a vector renderer can replace the PNG provider later. `MapScreen.h`: pan by drag, +/-, re-centre/follow GPS, Nearby nodes with a position as markers (tap = node detail), one tile decoded per loop pass. `maps/attribution.txt` is shown on the map. Planned split (user, 2026-09-25): a Nodes map (every contact with a position) and a separate Navigation map (waypoints + live shares only, for walking to a target). Tiles come from `tools/maps/fetch_tiles.py` (no default server: tile.openstreetmap.org blocks offline use) or on the device: the map's download button fetches the visible area (a few overview levels up to a chosen zoom) over WiFi (`map/TileDownloader.h`; skips tiles on the card, rejects non-PNG and placeholder answers; server from `maps/source.txt`, default OpenTopoMap). The HTTP GET runs on a worker task (`LvglPort.h`, keep-alive TLS); WiFi credentials (Settings > WiFi, with scan) live in NVS, and WiFi is on only during a download. Internal RAM is the constraint (Arduino-ESP32 2.0.17 / IDF 4.4: task stacks and, by default, mbedTLS buffers must be internal): with WiFi + Bluedroid up only ~13 KB was left, so the L2 LVGL env sets `MESH_IN_PSRAM` (`the_mesh`, ~120 KB, placement-new into PSRAM in `main.cpp`) and the fetch task points mbedTLS at PSRAM. The download popup shows IP, RSSI, free/largest internal heap and the last TLS/HTTP error. Arduino-ESP32 3.x (IDF 5: PSRAM stacks, NimBLE) is to be evaluated in the polishing phase. In the simulator the same code downloads through emscripten fetch.
 - PR #3381's LVGL UI is a reference for platform glue (flush, GT911, PSRAM pool) only; its screens are not adopted.
 
 ## Migration plan