docs: cover the new boards and !gps fix in solo-specific docs

README's Supported Devices table and Flashing section gain the
Cardputer ADV and T-Echo Lite + KeyShield rows/headings (both marked
experimental, matching release-notes.md and the Heltec V3/V4 entries).
external_keyboard.md gets a new section for their built-in TCA8418
keypads -- a separate mechanism from CardKB, not documented anywhere
before. settings_screen.md's GPS pwr row now lists !gps fix among the
things that hold GPS continuously on, matching the actual code.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/solo_features/external_keyboard.md

@@ -3,7 +3,9 @@
 [Go back](../../README.md)
 
 Two optional hardware add-ons, both auto-detected and both entirely optional — a
-build with them enabled runs exactly the same with nothing plugged in.
+build with them enabled runs exactly the same with nothing plugged in. Two of
+the newer boards also ship with their own **built-in** keypad instead —
+see [Built-in keyboards](#built-in-keyboards-cardputer-adv-t-echo-lite--keyshield).
 
 - **CardKB** — an M5Stack I2C QWERTY keyboard (address `0x5F`), for typing
   messages, names and labels without walking the on-screen letter grid.
@@ -17,8 +19,10 @@ build with them enabled runs exactly the same with nothing plugged in.
 | Seeed Wio Tracker L1 (OLED) | ✅ Grove connector | onboard |
 | Seeed Wio Tracker L1 (E-ink) | ✅ Grove connector | onboard |
 | GAT562 30S Mesh Kit | — | onboard |
-| Heltec V3 | ✅ solder to free GPIOs | ✅ solder to free GPIOs |
-| Heltec V4 | ✅ solder to free GPIOs | ✅ solder to free GPIOs |
+| Heltec V3 *(experimental)* | ✅ solder to free GPIOs | ✅ solder to free GPIOs |
+| Heltec V4 *(experimental)* | ✅ solder to free GPIOs | ✅ solder to free GPIOs |
+| M5Stack Cardputer ADV *(experimental)* | — | built-in keyboard instead, see below |
+| LilyGO T-Echo Lite + KeyShield *(experimental)* | — | built-in keypad instead, see below |
 
 ---
 
@@ -114,3 +118,19 @@ Everything above lives in the `[env:Heltec_v3_companion_solo_dual]` /
 and [`variants/heltec_v4/platformio.ini`](../../variants/heltec_v4/platformio.ini),
 with comments explaining which pins are safe to reuse. To build a CardKB-only
 device, comment out the joystick block and set Ext. KB to Compact.
+
+---
+
+## Built-in keyboards (Cardputer ADV, T-Echo Lite + KeyShield)
+
+*Experimental* — newly-added board support, not the CardKB/joystick add-ons
+above. Both keypads are TCA8418-based and share one polling path, entirely
+independent of the CardKB code — a board can have either, or neither.
+
+- **M5Stack Cardputer ADV** — built-in QWERTY, no CardKB or joystick needed.
+- **LilyGO T-Echo Lite + KeyShield** — the KeyShield add-on gives the T-Echo
+  Lite a T9 keypad; without it the board has no usable input for the solo UI.
+
+Neither keypad follows CardKB's exact Fn-shortcut table (Fn+Enter,
+Fn+letter accent popups, Tab, Fn+Esc lock) — see each board's own
+`platformio.ini` / keyboard driver under `variants/` for its current keymap.

docs/solo_features/settings_screen/settings_screen.md

@@ -90,7 +90,7 @@ The **repeater** mode and its flood filters live on their own screen — see **T
 | Name        | keyboard entry (up to 31 chars)                     | This device's node name, shown to others and in every advert. **Enter** opens the keyboard pre-filled with the current name; applied and saved on submit |
 | Timezone    | −12 h … +14 h                                       | UTC offset in whole hours                                                              |
 | Low battery | off / 3.0 V / 3.1 V / 3.2 V / 3.3 V / 3.4 V / 3.5 V | Auto-shutdown threshold; also sets the 0 % anchor for the battery percentage indicator |
-| GPS pwr _(if GPS detected)_ | off / 1 min / 5 min / 15 min / 30 min / 1 h | **Battery saver.** Cycles GPS off between fixes instead of running it continuously; each wake waits for a fix (up to 60 s) before sleeping again for the chosen interval. Automatically stays continuously on regardless of this setting whenever something needs a live position — an active Trail recording, Map › Live share, an armed Locator, or the Compass / Nearby navigate view. `off` (default) matches earlier releases: GPS runs continuously whenever enabled. The GPS status icon blinks while napping between fixes. |
+| GPS pwr _(if GPS detected)_ | off / 1 min / 5 min / 15 min / 30 min / 1 h | **Battery saver.** Cycles GPS off between fixes instead of running it continuously; each wake waits for a fix (up to 60 s) before sleeping again for the chosen interval. Automatically stays continuously on regardless of this setting whenever something needs a live position — an active Trail recording, Map › Live share, an armed Locator, the Compass / Nearby navigate view, or an in-flight `!gps fix` bot request. `off` (default) matches earlier releases: GPS runs continuously whenever enabled. The GPS status icon blinks while napping between fixes. |
 | Units       | Metric / Imperial                                   | Global unit system for every distance/speed shown in Tools (Nearby Nodes, Trail, navigate-to-point). Metric: m / km, km/h, min/km. Imperial: ft / mi, mph, min/mi |
 | Reboot      | action (**Enter**)                                  | Restarts this device. Pending setting changes are saved first. Last row, so it isn't the default-selected one |