badges: hide the Source badge when the source has no panel of its own

A Source pill that opens nothing (UDPS, Flat UDP, files) was noise. It is now shown only while the slide-over has a source page; the [badges] source line gains visible=.

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

docs/claude/architecture.md

@@ -113,7 +113,9 @@ touching the data path.
   **Source** badges). `sync_signal_badges()` rebuilds the signal badges (from `rebuild_signal_panels()`);
   their order is `App::badge_order`, in memory only. A badge is a flat button whose `page` is the slide-over page it
   toggles; the Source badge's page is the first `source-*` page, and a kind with none (UDPS, Flat UDP, a
-  file) leaves it a read-out with `can_target` off.
+  file) leaves it **hidden** (the user asked for hide here, not the usual disable): `sync_badge_bar()` sets its visibility,
+  pick and focus from `slideover.source_pages` being non-empty every tick, so anything that indexes the badge
+  (the tour's `badges` step targets the whole bar, `[badges]`) must tolerate it being absent.
 - **The dock** is the `AdwOverlaySplitView` sidebar (`side_box` > `dock_scroller` > `dock_page`): the
   cursors and the measurements only, in one scroller (the signal list is the `signals` page). It holds no tab switcher and no
   revealer, and it does not hold a source kind's panels (those are slide-over pages).