feat(studio): channel pill in sidebar + Featured strip in Store (v0.20.0)

Sidebar:
- New active-channel pill below the connection pill,
  color-coded so production deployments look visibly
  different from local-dev. Click opens Settings; tooltip
  explains the channel taxonomy. Polled in lockstep with the
  health probe so it tracks CLI-driven `fai channel switch`.

Store:
- Featured strip above the main grid renders editorial
  picks as bigger hero tiles with a subtle gradient
  backdrop, version + status pills, and a one-click
  Install. Hidden the moment the operator types in the
  search box or picks any filter — the result list is the
  answer they want, not editorial chrome.

StoreItem now carries the `featured` flag so the page can
filter without an extra round-trip.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

pubspec.yaml

@@ -1,7 +1,7 @@
 name: fai_studio
 description: "F∆I Studio — desktop GUI for the F∆I hub"
 publish_to: 'none'
-version: 0.19.0
+version: 0.20.0
 
 environment:
   sdk: ^3.11.0-200.1.beta