heather: homepage fixes - bookmark href format, jitsi-meet icon, teable favicon

bookmarks.yaml needs href: key (was bare URL → new URL() crash).
jitsi.png -> jitsi-meet.png (proper brand icon in dashboard-icons).
teable has no dashboard-icons entry -> use teable.iscg.dev/favicon.ico.

hosts/heather/arion-compose.nix

@@ -47,7 +47,7 @@ let
             href: https://chat.iscg.dev
             description: Matrix web client
         - Jitsi Meet:
-            icon: jitsi.png
+            icon: jitsi-meet.png
             href: https://jitsi.iscg.dev
             description: Video conferencing
     - Productivity:
@@ -56,7 +56,7 @@ let
             href: https://note.iscg.dev
             description: Notes wiki (herbarium)
         - Teable:
-            icon: teable.png
+            icon: https://teable.iscg.dev/favicon.ico
             href: https://teable.iscg.dev
             description: No-code database
   '';
@@ -87,7 +87,8 @@ let
   homepageBookmarksYaml = pkgs.writeText "homepage-bookmarks.yaml" ''
     - Forge:
         - nix-config:
-            - https://git.iscg.dev/mikl/nix-config
+            - abbr: Nx
+              href: https://git.iscg.dev/mikl/nix-config
   '';
 
 in