feat(deps): add cargo as a managed dependency with rustup installer

cargo is now the second entry in the catalog (after fish) so it is
installed before any Rust tool that depends on it. Install preference:
rustup installer (curl | sh) first, system PM as fallback. Update
runs rustup update when rustup is available.

The rustup-installer special is evaluated before the system PM in the
method list so it is always option 1 / the default for cargo.

functions/_fish_deps_catalog.fish

@@ -2,38 +2,40 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
 # Populates parallel arrays describing every managed dependency.
-# Callers must invoke this function before accessing _fdc_* variables.
+# Callers must invoke this function before accessing _fdc_* arrays.
 #
 # Array layout (same index across all sets):
 #   _fdc_bins    — binary name (what `type -q` checks)
 #   _fdc_tiers   — req | int | rec
 #   _fdc_cargo   — cargo crate name, or "" if not on crates.io
 #   _fdc_pm      — system PM package name, or "" if not in repos
-#   _fdc_special — special install key: fisher-bootstrap | fzf-update |
-#                  pipx | curl-installer | "" (none)
+#   _fdc_special — special install key: rustup-installer | fisher-bootstrap |
+#                  fzf-update | paru-build | pipx | curl-installer | "" (none)
+#
+# cargo is listed second so it is installed before Rust tools that depend on it.
 function _fish_deps_catalog
     set -g _fdc_bins \
-        fish fisher starship fzf zoxide direnv paru \
+        fish cargo fisher starship fzf zoxide direnv paru \
         wakatime tailscale \
         eza lsd bat btop dust duf prettyping most rg lazygit lazydocker trash kitty wezterm
 
     set -g _fdc_tiers \
-        req req req req req req rec \
+        req req req req req req req rec \
         int int \
         rec rec rec rec rec rec rec rec rec rec rec rec rec rec
 
     set -g _fdc_cargo \
-        "" "" starship "" zoxide "" "" \
+        "" "" "" starship "" zoxide "" "" \
         "" "" \
         eza lsd bat "" du-dust "" "" "" ripgrep "" "" trash-cli "" ""
 
     set -g _fdc_pm \
-        fish "" starship fzf zoxide direnv "" \
+        fish cargo "" starship fzf zoxide direnv "" \
         wakatime tailscale \
         eza lsd bat btop dust duf prettyping most ripgrep lazygit lazydocker trash kitty wezterm
 
     set -g _fdc_special \
-        "" fisher-bootstrap curl-installer fzf-update "" "" paru-build \
+        "" rustup-installer fisher-bootstrap curl-installer fzf-update "" "" paru-build \
         pipx "" \
         "" "" "" "" "" "" "" "" "" "" "" "" "" ""
 end

functions/_fish_deps_install.fish

@@ -20,25 +20,31 @@ function _fish_deps_install
             set -l methods
             set -l method_labels
 
-            # Cargo first — preferred for Rust tools; gets the latest crate version
+            # Cargo — preferred for Rust tools; gets the latest crate version
             if test -n "$cargo_crate"
                 if type -q cargo
                     set -a methods cargo
                     set -a method_labels "cargo ($cargo_crate)"
                 else
                     set_color brblack
-                    echo "  note: cargo not found — install rustup for the latest $bin"
+                    echo "  note: cargo not found — install cargo first for the latest $bin"
                     set_color normal
                 end
             end
 
-            # System PM — after cargo so cargo is always the default when available
+            # rustup installer — listed before system PM so it is the default for cargo itself
+            if test "$special" = rustup-installer
+                set -a methods special-rustup
+                set -a method_labels "rustup installer (curl | sh)"
+            end
+
+            # System PM — after cargo/rustup so those are always the default when available
             if test -n "$pm_pkg"; and test -n "$pm"
                 set -a methods pm
                 set -a method_labels "$pm ($pm_pkg)"
             end
 
-            # Special methods
+            # Remaining special methods
             switch $special
                 case fzf-update
                     set -a methods special-fzf
@@ -108,6 +114,8 @@ function _fish_deps_install
                     cargo install $cargo_crate
                 case pm
                     _fish_deps_pm_install $pm_pkg
+                case special-rustup
+                    curl https://sh.rustup.rs -sSf | sh
                 case special-fzf
                     fzf-update
                 case special-fisher

functions/_fish_deps_update.fish

@@ -28,6 +28,17 @@ function _fish_deps_update
         set -l pm_pkg       $_fdc_pm[$i]
         set -l special      $_fdc_special[$i]
 
+        # cargo: update via rustup
+        if test "$special" = rustup-installer
+            if type -q rustup
+                echo "Updating $bin..."
+                rustup update
+                set updated_any 1
+            end
+            set i (math $i + 1)
+            continue
+        end
+
         # fzf: always use fzf-update (git-based)
         if test "$special" = fzf-update
             echo "Updating $bin..."