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>

clicker/focus.py

@@ -12,6 +12,8 @@ which it is, because that's where this script was launched — Chrome as a whole
 still in the background. This module raises the application itself.
 """
 
+import os
+import shutil
 import subprocess
 import sys
 import time
@@ -26,35 +28,48 @@ BROWSERS = {
                    "com.google.Chrome.dev", "com.google.Chrome.canary",
                    "org.chromium.Chromium"),
         "win32": ("chrome.exe",),
+        "linux": ("google-chrome", "chromium", "chromium-browser", "google-chrome-stable"),
         "titles": ("Chrome", "Chromium"),
     },
     "edge": {
         "darwin": ("com.microsoft.edgemac",),
         "win32": ("msedge.exe",),
+        "linux": ("microsoft-edge", "msedge"),
         "titles": ("Edge",),
     },
     "brave": {
         "darwin": ("com.brave.Browser",),
         "win32": ("brave.exe",),
+        "linux": ("brave-browser", "brave"),
         "titles": ("Brave",),
     },
     "opera": {
         "darwin": ("com.operasoftware.Opera",),
         "win32": ("opera.exe", "launcher.exe"),
+        "linux": ("opera",),
         "titles": ("Opera",),
     },
     "vivaldi": {
         "darwin": ("com.vivaldi.Vivaldi",),
         "win32": ("vivaldi.exe",),
+        "linux": ("vivaldi-stable", "vivaldi"),
         "titles": ("Vivaldi",),
     },
 }
 
 
+def _platform_key() -> str:
+    if sys.platform == "darwin":
+        return "darwin"
+    if sys.platform.startswith("linux"):
+        return "linux"
+    return "win32"
+
+
 def _ids_for(browser: str | None) -> tuple[str, ...]:
     """Identifiers to accept on this platform. Without a named browser, every
     known one — the old behaviour, and still right on a single-browser box."""
-    key = "darwin" if sys.platform == "darwin" else "win32"
+    key = _platform_key()
     if browser and browser in BROWSERS:
         return BROWSERS[browser][key]
     return tuple(i for b in BROWSERS.values() for i in b[key])
@@ -142,9 +157,67 @@ def _mac_workspace():
     return NSWorkspace.sharedWorkspace()
 
 
+def _linux_session_problem() -> str | None:
+    """Why the clicker cannot drive this desktop, or None if it can.
+
+    Raspberry Pi OS on a Pi 5 defaults to Wayland (labwc). Neither xdotool nor
+    pyautogui works there: both speak X11 protocol, and Wayland deliberately
+    refuses to let one client synthesise input into another or read the focused
+    window. There is no workaround short of switching the session to X11, so say
+    so plainly rather than failing every step with something cryptic.
+    """
+    if not os.environ.get("DISPLAY"):
+        if os.environ.get("WAYLAND_DISPLAY"):
+            return ("this is a Wayland session and the clicker needs X11 — on Raspberry Pi OS: "
+                    "sudo raspi-config -> Advanced Options -> Wayland -> X11, then reboot")
+        return "no DISPLAY is set — the clicker needs a graphical session"
+    if shutil.which("xdotool") is None:
+        return "xdotool is not installed — run: sudo apt install -y xdotool"
+    return None
+
+
+def _xdotool(*args: str) -> subprocess.CompletedProcess:
+    return subprocess.run(["xdotool", *args], capture_output=True, text=True, timeout=5)
+
+
+def _linux_frontmost() -> str | None:
+    """WM_CLASS of the focused window, lowercased to match the ids above."""
+    try:
+        result = _xdotool("getactivewindow", "getwindowclassname")
+    except Exception:
+        return None
+    name = (result.stdout or "").strip().lower()
+    return name or None
+
+
+def _linux_activate(browser: str | None = None) -> FocusResult:
+    problem = _linux_session_problem()
+    if problem:
+        return FocusResult(False, problem)
+
+    for cls in _ids_for(browser):
+        try:
+            found = _xdotool("search", "--onlyvisible", "--class", cls)
+        except Exception as exc:
+            return FocusResult(False, f"xdotool failed ({exc})")
+
+        ids = (found.stdout or "").split()
+        if not ids:
+            continue
+
+        # Last match is the most recently mapped window — the one a person would
+        # mean by "the browser" when several are open.
+        activated = _xdotool("windowactivate", "--sync", ids[-1])
+        if activated.returncode == 0:
+            return FocusResult(True, f"activated {cls} (window {ids[-1]})")
+        return FocusResult(False, f"could not activate {cls}: {(activated.stderr or '').strip()}")
+
+    return FocusResult(False, f"no {browser or 'browser'} window found")
+
+
 def browser_ids(browser: str | None = None) -> tuple[str, ...]:
     """What counts as "the browser" on this platform, optionally narrowed to one."""
-    if sys.platform in ("darwin", "win32"):
+    if sys.platform in ("darwin", "win32") or sys.platform.startswith("linux"):
         return _ids_for(browser)
     return ()
 
@@ -172,6 +245,9 @@ def frontmost() -> str | None:
         except Exception:
             return None
 
+    if sys.platform.startswith("linux"):
+        return _linux_frontmost()
+
     return None
 
 
@@ -257,7 +333,12 @@ def activate_browser(browser: str | None = None) -> FocusResult:
     it, any known browser will do — fine on a machine with one installed, wrong
     on a machine with two.
     """
-    result = _mac_activate(browser) if sys.platform == "darwin" else _other_activate(browser)
+    if sys.platform == "darwin":
+        result = _mac_activate(browser)
+    elif sys.platform.startswith("linux"):
+        result = _linux_activate(browser)
+    else:
+        result = _other_activate(browser)
     if result.ok:
         time.sleep(SETTLE)
     return result