config(fish): add full fish config from live home; portable clipboard + env guards

Keep starship prompt (omp migration rejected). cpy/pst aliases branch on
wl-copy vs pbcopy; functions use the aliases. BROWSER/CHROME_EXECUTABLE
guarded on binary existence. auto-Niri.fish and cp-appid.fish are
linux-only (gated in .chezmoiignore).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.chezmoidata/packages.yaml

@@ -41,8 +41,8 @@ packages:
       - glow
       - atuin
       - wget
-    aur:
-      - oh-my-posh-bin
+      - starship
+    aur: []
     desktop:
       # linux desktop layer (role desktop|laptop)
       pacman:
@@ -80,7 +80,7 @@ packages:
       - gum
       - glow
       - atuin
-      - oh-my-posh
+      - starship
     cask:
       - kitty
   shared: