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>

README.md

@@ -118,10 +118,11 @@ place (it opens the list, and `+` is hidden): the E-1608's 8 analog inputs and c
 otherwise. The signal badges sit in a scroller, so the bar's minimum width, and with it the window's,
 never depends on how many signals there are. The badge order is kept **for the session only**; it is not
 written to the session file. The right-hand end carries two words-only badges: **Trigger** (`off`, `armed`, `capturing`, `triggered`
-or `disarmed`) and **Source** (the kind's name only -- the link state is the status bar's; a read-out, not a button,
-for a source with no controls of its own, and for a file). A badge opens the **slide-over**: a 360 px
+or `disarmed`) and **Source** (the kind's name only -- the link state is the status bar's). **Source is shown only when the source
+has panels of its own** (the E-1608's); for UDPS, Flat UDP and a file there is nothing for it to open, so it is hidden
+(the bar keeps its height; the kind's name is in the status bar). A badge opens the **slide-over**: a 360 px
 panel laid over the plot's right edge, opaque, with its own title, a *Close* button and one scroller per
-page. The Trigger badge opens the trigger form; the Source badge opens the source kind's own panels
+page. The Trigger badge opens the trigger form; the Source badge (when shown) opens the source kind's own panels
 (the E-1608's *Analog out* and *Digital I/O*, behind a segmented switch at the top of the panel). It
 closes with a second click on its badge, with `Esc`, with *Close*, or with a click on the plot; it never
 resizes the plot. The right-hand **dock** (the existing sidebar, 320 px) holds what is left of the old