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/__init__.py

@@ -0,0 +1,30 @@
+"""Cross-platform helper for reading the front browser tab's URL.
+
+This is the one genuinely OS-specific piece. Reading *your own* browser's
+current URL is a passive, local operation (no request to the target site), so
+it stays within the screen-capture / compliance posture. When it can't return
+a URL (common on Windows/Linux), the detector falls back to reading the address
+bar visually from a screenshot via the AI.
+"""
+import sys
+from typing import Optional
+
+
+def get_active_tab_url() -> Optional[str]:
+    """Best-effort URL of the frontmost browser tab, or None if unavailable."""
+    try:
+        if sys.platform == "darwin":
+            from . import macos
+
+            return macos.get_active_tab_url()
+        if sys.platform.startswith("linux"):
+            from . import linux
+
+            return linux.get_active_tab_url()
+        if sys.platform in ("win32", "cygwin"):
+            from . import windows
+
+            return windows.get_active_tab_url()
+    except Exception:
+        return None
+    return None