Initial commit: Screen Leads app

Screen-capture lead tool: capture agent, Claude vision extractor with
pluggable site recipes (LinkedIn), canonical funnel model, SQLite storage,
FastAPI backend, dashboard, and setup/run scripts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/platform/linux.py

@@ -0,0 +1,11 @@
+"""Linux (X11): the active window *title* is reachable via xdotool, but the URL
+is not exposed without a browser extension or the accessibility bus. We return
+None so the detector falls back to reading the address bar visually from the
+screenshot, which is the portable path. (Wayland exposes neither; the app warns
+about that separately.)
+"""
+from typing import Optional
+
+
+def get_active_tab_url() -> Optional[str]:
+    return None