Add Linux/Raspberry Pi setup and port the clicker to X11

The clicker had no Linux support at all: pygetwindow has no X11 backend, so
_other_activate returned "window management is unsupported" and every step
failed before it could click. focus.py now has a third backend that raises the
browser with xdotool and reads the focused window's WM_CLASS to verify it came
forward - the same activate-then-confirm shape as the macOS and Windows paths.

setup-linux.sh mirrors setup-windows.bat with apt instead of winget. Three
things are specific to this platform rather than incidental:

- Node comes from NodeSource. Pi OS ships one too old for Next 16, and the LTS
  line is also what better-sqlite3 publishes prebuilt arm64 binaries for.
- Python dependencies go in a virtualenv. Pi OS Bookworm enforces PEP 668, so
  pip into the system interpreter fails with externally-managed-environment.
- Autostart uses an XDG ~/.config/autostart entry, the direct analogue of the
  Windows Startup folder: no sudo, and it runs inside the graphical session,
  which the clicker needs for DISPLAY.

Wayland is called out in four places - the session guard, diagnose.py, the
installer and both READMEs - because Pi OS on a Pi 5 defaults to it and the
clicker simply cannot work there. Wayland does not let one client synthesise
input into another, so this is a switch-to-X11 situation, not a bug to fix.

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

README.md

@@ -6,8 +6,9 @@ Automated futures trading dashboard for prop firm accounts via Tradovate.
 
 ## Setup
 
-On a fresh Windows machine, in **PowerShell**, from wherever you want the
-instance to live:
+### Windows
+
+In **PowerShell**, from wherever you want the instance to live:
 
 ```powershell
 irm https://git.juicerroom.com/senofy/autofirmer-expanded/raw/branch/master/setup-windows.bat -OutFile setup-windows.bat
@@ -34,6 +35,33 @@ Two things it deliberately does, worth knowing:
   needed — or installed without its "add to PATH" option — is invisible to a
   running shell, so the script checks the standard install directories too.
 
+### Raspberry Pi 5 / Debian / Ubuntu
+
+```bash
+curl -fsSLO https://git.juicerroom.com/senofy/autofirmer-expanded/raw/branch/master/setup-linux.sh
+```
+
+```bash
+bash setup-linux.sh
+```
+
+Same idea, apt instead of winget. It installs Node 22 from NodeSource (Pi OS
+ships one too old for Next 16), `xdotool` and `scrot` for the clicker, and puts
+the Python dependencies in a virtualenv — Pi OS Bookworm enforces PEP 668, so a
+system-wide `pip install` fails outright.
+
+**The clicker needs X11.** Pi OS on a Pi 5 defaults to Wayland, which does not
+let one client synthesise input into another or read the focused window, so
+neither `xdotool` nor pyautogui can work there. The dashboard is unaffected, but
+for the AutoBuyer:
+
+```bash
+sudo raspi-config    # Advanced Options -> Wayland -> X11, then reboot
+```
+
+`python clicker/diagnose.py` reports the session type, `DISPLAY` and whether
+`xdotool` is present — run it before trusting a new machine.
+
 The dashboard runs on port **3000**: `http://localhost:3000`.
 
 ---