docs: stage I3 -- documentation rewritten under docs/solo

Short pages by feature (getting started, messages, contacts, navigation,
tools, settings, lock, hardware) instead of one page per OLED screen, with
Wio Tracker L2 differences as notes; facts checked against the code
(keyboard scripts vs. hold-for-accents, {batt}/{dist}, L2 limits and
settings layout). Developer guides and build flags under docs/solo/developer.
Old docs/solo_features and its ~50 screenshots removed; a hero banner and
three simulator screenshots added; links updated.

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

docs/solo/hardware.md

@@ -0,0 +1,99 @@
+# Hardware
+
+## External keyboard and joystick
+
+Two optional add-ons, detected at boot; a build with them enabled works the
+same with nothing plugged in.
+
+| Device | CardKB | Wired joystick |
+| ------ | :----: | :------------: |
+| Wio Tracker L1 (OLED / e-ink) | Grove connector | built in |
+| GAT562 30S Mesh Kit | — | built in |
+| Heltec V3 / V4 | soldered (below) | soldered (below) |
+| ProMicro | on the main I2C bus (required: it has no buttons) | — |
+| Cardputer ADV, T-Echo Lite + KeyShield | built-in keyboard instead | — |
+
+### CardKB
+
+An M5Stack CardKB types straight into any text field. It sends plain
+characters, so the keyboard alphabet settings don't apply to it.
+
+| Key | Does |
+| --- | ---- |
+| Arrows, Enter, Esc | Same as the joystick, Enter and Back |
+| Backspace | Deletes before the cursor |
+| **Fn+Enter** | Submits the field |
+| **Fn+letter** | Accents for that letter (Fn+A → á à ä…) |
+| **Tab** | Hold Enter (options menus) |
+| **Fn+Esc** | Locks / unlocks the screen |
+
+Settings › Keyboard › **Ext. KB**: **Full** keeps the on-screen grid, so the
+CardKB and the joystick can be mixed; **Compact** hides it, the arrows move the
+text cursor and Enter submits. Compact needs no joystick at all.
+
+### Wired joystick
+
+Four direction contacts and a press contact (Enter), each shorted to ground
+when pressed; the firmware enables the pull-ups, so no resistors are needed.
+The board's own button becomes Back. Settings › Display › **Joystick
+rotation** turns the directions for a stick mounted sideways.
+
+### Wiring on the Heltec V3 / V4
+
+Neither board has a joystick or a keyboard connector, so both are soldered to
+free pins. V3 and V4 use the same pins (confirmed on a V4).
+
+| Function | GPIO |
+| -------- | :--: |
+| CardKB SDA / SCL | 3 / 4 (second I2C bus, not the display's) |
+| Joystick up / down / left / right | 23 / 6 / 47 / 48 |
+| Joystick press (Enter) | 33 |
+| Back | 0 (the PRG button, nothing to wire) |
+
+The pins are set in [`solo/heltec_v3/platformio.ini`](../../solo/heltec_v3/platformio.ini)
+and [`solo/heltec_v4/platformio.ini`](../../solo/heltec_v4/platformio.ini).
+For a CardKB-only build, comment out the joystick block there and use
+Ext. KB = Compact.
+
+### Built-in keyboards
+
+The Cardputer ADV has a QWERTY keyboard, the T-Echo Lite a T9 keypad on its
+KeyShield add-on (without it the board has no usable input). Their keymaps
+are in each board's driver under `variants/`; they don't follow the CardKB's
+Fn shortcuts.
+
+## E-ink
+
+The e-ink Wio Tracker L1 (250 × 122) has a few settings of its own in
+Settings › Display:
+
+- **Rotation**: landscape or portrait, applied at once; every screen reflows.
+- **Joystick rotation**, independent of the display's.
+- **Full refresh**: how many partial updates between full ones, against
+  ghosting.
+
+Clock seconds are hidden by default, and live timers refresh coarsely, to
+spare the panel.
+
+## Wio Tracker L2
+
+- **Buttons**: the top one turns the screen off and on; the side one goes
+  home, and held and let go mutes the sound. Side + top takes a screenshot.
+  Holding the side button in the first seconds after power-on starts the CLI
+  rescue on USB serial.
+- **SD card**: holds the message history, maps, GPX trails and live map tiles.
+  Settings › Storage shows what takes the space, how many messages each
+  conversation keeps, and deletes the history.
+- **USB drive**: plugged into a computer, the device asks whether to only
+  charge or to lend the computer the SD card. While lent, the device can't use
+  the card; eject it on the computer and the device restarts. With a screen
+  PIN set, it doesn't ask until the screen is unlocked.
+- **WiFi**: used only for map downloads, live tiles and updates, and off the
+  rest of the time. Settings › WiFi saves several networks and joins the
+  strongest; the WiFi switch in Settings forbids it entirely.
+
+## Build flags
+
+Extra hardware (a buzzer, a vibration motor, a Hall sensor for a magnetic
+cover, GPIO, an external PA) is enabled with build flags in your own
+`solo/<board>/platformio.ini`; see [Build flags](./developer/build-flags.md).