docs(#359): wire redesign hero into 1.2.0 notes, drop other placeholders

Hero image (SHA-pinned raw URL, resolves now + at release) at the top;
removed the pinned-rail and FEM-LNA placeholders per Ben (one deliberate
hero, no empty slots).

Agent: SapphireCompass (session 8d755b5e)

release-notes/1.2.0.md

@@ -5,7 +5,7 @@ hood, GIFs that work across every MeshCore client, and hands-on control of your
 radio's RF front end. This is also the first Offband release built, signed, and
 shipped to every platform automatically.
 
-<!-- SCREENSHOT: hero shot of the redesigned app (pinned left rail + a channel open) -->
+![Offband Meshcore 1.2.0 on Windows: the redesigned interface with the navigation rail pinned open alongside a channel](https://raw.githubusercontent.com/OffbandMesh/meshcore-client/3826b7372122f812cc54d4f5bae438581ad78240/docs/releases/1.2.0/redesign.png)
 
 ### One app, every platform
 
@@ -32,8 +32,6 @@ that finally gets out of your way.
   panel, and the back button finally behaves the way it should: it backgrounds
   the app instead of killing it, and never knocks you off a connected radio.
 
-<!-- SCREENSHOT: left rail pinned open, showing the channel list -->
-
 ### Your data, on solid ground
 
 Under the surface, Offband now keeps your messages, contacts, and channels in a
@@ -68,8 +66,6 @@ amplifier that shape receive sensitivity and transmit path).
 Both are gated on firmware capability, so they appear only where the radio
 actually supports them.
 
-<!-- SCREENSHOT: Radio Settings showing the FEM LNA toggle -->
-
 ### Deeper diagnostics
 
 More signal, less guesswork when you need to see what your mesh is doing.