feat(deps): add fish-deps unified dependency management command

Introduces `fish-deps` with four subcommands:
- status: colored installed/missing report per tier (required/integrations/recommended)
- install: interactively install each missing dep, prompts method when multiple exist
- update: update all installed deps using their preferred method
- sync: install missing then update installed

Install method priority: cargo (Rust tools get latest crate) > system PM
(paru/pacman/apt/brew/pkg/dnf/yum) > git clone (fzf via fzf-update) >
curl installer (starship, fisher) > pipx (wakatime).

Splits into focused helper files:
- _fish_deps_catalog.fish: parallel-array dep catalog with tiers, cargo crates, PM names, special install keys
- _fish_deps_pm.fish: PM detection and install/upgrade helpers
- _fish_deps_status.fish: tier-grouped colored status display
- _fish_deps_install.fish: per-dep interactive install with method selection
- _fish_deps_update.fish: per-dep update using known install method

check_fish_deps becomes a thin wrapper delegating to `fish-deps status`.
README updated with Dependency Management section.

functions/fish-deps.fish

@@ -0,0 +1,41 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+function fish-deps --description 'Manage fish shell dependencies'
+    set -l subcmd $argv[1]
+
+    switch $subcmd
+        case status ''
+            _fish_deps_status
+        case install
+            _fish_deps_install
+        case update
+            _fish_deps_update
+        case sync
+            echo "=== Installing missing deps ==="
+            _fish_deps_install
+            echo ""
+            echo "=== Updating installed deps ==="
+            _fish_deps_update
+        case '*'
+            set_color red
+            echo "Unknown subcommand: $subcmd"
+            set_color normal
+            echo ""
+            __fish_deps_help
+            return 1
+    end
+end
+
+function __fish_deps_help
+    set_color cyan; echo "fish-deps — manage fish shell dependencies"; set_color normal
+    echo ""
+    echo "Usage:"
+    echo "  fish-deps [status]   Check installed/missing deps (default)"
+    echo "  fish-deps install    Install missing deps interactively"
+    echo "  fish-deps update     Update all installed deps"
+    echo "  fish-deps sync       Install missing, then update all"
+    echo ""
+    echo "Install method priority: cargo > system PM > git/curl/pipx"
+    echo "When multiple methods are available, you will be prompted to choose."
+end