docs: clarify that plugin functionality is bundled, not managed by fisher

Only jorgebucaran/fisher itself is in fish_plugins. The functionality
from catppuccin/fish, fzf.fish, done, autopair, and puffer-fish is
bundled directly with this config in modified form and must not be
installed or updated via fisher.

Removes sponge (not present), corrects file path mappings for bundled
components, fixes stale "Plugin sync failed" message in first_run.fish,
and expands fish-config.index with missing sections 9–11.

conf.d/first_run.fish

@@ -35,7 +35,7 @@ if not type -q fisher
     if curl -sL https://raw.githubusercontent.com/jorgebucaran/fisher/main/functions/fisher.fish | source
         echo "  [first-run] Fisher installed."
         if not fisher update 2>/dev/null
-            echo "  [first-run] Plugin sync failed — run 'fisher update' manually." >&2
+            echo "  [first-run] Fisher update failed — run 'fisher update' manually." >&2
         end
     else
         echo "  [first-run] Fisher install failed — run 'fisher update' manually." >&2