e1608: probe and docs for the network scan

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/claude/architecture.md

@@ -44,7 +44,9 @@ What feeds `Acquisition` is a `DataSource`, one of the registered *kinds*.
   has neither key, so a legacy session is read as UDPS and nothing existing moves.
 - **The E-1608 kind has three layers, and only the top one knows the framework.** `e1608_link`
   (discovery, handshake, framed TCP commands, the scan socket) and `e1608_device` (typed commands,
-  factory calibration, `decode_scans`) are plain POSIX C++ with no GTK or `DataSource` types;
+  factory calibration, `decode_scans`) are plain POSIX C++ with no GTK or `DataSource` types; discovery is
+  `Scan` (one socket per interface, polled by the caller: the form polls it from a GLib timer on the main
+  thread, the source's lookup goes through `discover_broadcast`);
   `e1608_source` is the `DataSource`; `e1608_kind` and `e1608_panels` are the UI. A change to the wire
   never reaches the UI files.
 - The E-1608 source runs **everything inside `poll()`** on the producer thread: posted commands, the