feat(fish-deps): add uv as managed dep; install before cargo and fish

uv is now listed first in the catalog (before cargo and fish) so it is
installed automatically before the fish source build is attempted.
Install uses the official curl script; update uses `uv self update`.

Catalog order is now: uv → cargo → fish → … ensuring prerequisites are
in place before any dependent install method runs.

README updated: uv and cargo added to the Required table, warning callout
and dependency management note reflect the automatic install flow.

functions/_fish_deps_update.fish

@@ -93,6 +93,15 @@ function _fish_deps_update
             continue
         end
 
+        # uv: use built-in self-updater
+        if test "$special" = curl-uv
+            echo "Updating $bin..."
+            uv self update
+            set updated_any 1
+            set i (math $i + 1)
+            continue
+        end
+
         # fish: prefer build from source via git + cargo; fall back to PM
         if test "$special" = git-cargo-fish
             if type -q cargo; and type -q uv