Redesign the Manage window and fold About into it as a tab

The previous layout was a fixed 460x360 window regardless of tab or
state, with a plain unbordered table and text +/- buttons — it read as a
generic cross-platform port rather than something native. Several rows
also had no real width anchor at all, so they floated: flush against the
window's left edge with no margin, and in the add form's case wide enough
to overflow past the right edge.

- The window is no longer manually resizable. Each tab reports its own
  preferredContentSize, recomputed in viewDidLayout and after every state
  change, and NSTabViewController resizes the window to match. That is
  what actually fixes the large empty areas: a tab with less content gets
  a smaller window rather than sitting inside a fixed larger one.
- Every row now anchors its width to the one element with a real absolute
  width, fixing both the edge-touching and the overflow.
- Table gains a bezel border and alternating rows; form labels get a
  fixed trailing-aligned width so fields line up; the error label wraps
  instead of truncating; tab padding is consistent.
- About moves out of a separate panel into a third tab, with the app icon
  centred and enlarged to 96px.

Verified visually with a standalone harness that drives the real window
and screenshots it, rather than simulating input — scripting clicks into
the app itself needs an Accessibility grant this environment lacks.

.github/workflows/release.yml

@@ -28,6 +28,12 @@ jobs:
 
       - name: Build shannoncoat.app
         run: ./build.sh
+        env:
+          # This workflow only ever runs against a tag (see the trigger
+          # comment above) — told to build.sh directly rather than having
+          # it re-derive that via `git describe`, which needs full tag
+          # refs a CI runner's checkout isn't guaranteed to have fetched.
+          SHANNONCOAT_RELEASE_BUILD: "1"
 
       - name: Zip app bundle
         run: ditto -c -k --sequesterRsrc --keepParent ".build/shannoncoat.app" "shannoncoat.app.zip"