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_update.fish

@@ -0,0 +1,84 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+# Update all installed deps using their known install method.
+# Priority: cargo > system PM > special (fzf-update, fisher, pipx).
+function _fish_deps_update
+    _fish_deps_catalog
+
+    set -l pm (_fish_deps_detect_pm)
+    set -l updated_any 0
+
+    # Fisher plugins — always update if fisher is present
+    if type -q fisher
+        echo "Updating fisher plugins..."
+        fisher update
+        set updated_any 1
+    end
+
+    set -l i 1
+    for bin in $_fdc_bins
+        # Skip fisher itself (handled above) and tools that aren't installed
+        if test "$bin" = fisher -o not (type -q $bin)
+            set i (math $i + 1)
+            continue
+        end
+
+        set -l cargo_crate  $_fdc_cargo[$i]
+        set -l pm_pkg       $_fdc_pm[$i]
+        set -l special      $_fdc_special[$i]
+
+        # fzf: always use fzf-update (git-based)
+        if test "$special" = fzf-update
+            echo "Updating $bin..."
+            fzf-update
+            set updated_any 1
+            set i (math $i + 1)
+            continue
+        end
+
+        # pipx tools
+        if test "$special" = pipx
+            if type -q pipx
+                echo "Updating $bin..."
+                pipx upgrade $bin
+                set updated_any 1
+            end
+            set i (math $i + 1)
+            continue
+        end
+
+        # curl-installer tools (starship etc.): re-run install script, which upgrades in place
+        if test "$special" = curl-installer
+            if test "$bin" = starship
+                echo "Updating $bin..."
+                curl -sS https://starship.rs/install.sh | sh -- --yes
+                set updated_any 1
+            end
+            set i (math $i + 1)
+            continue
+        end
+
+        # Cargo: prefer for Rust tools
+        if test -n "$cargo_crate" -a (type -q cargo)
+            echo "Updating $bin..."
+            cargo install --force $cargo_crate
+            set updated_any 1
+            set i (math $i + 1)
+            continue
+        end
+
+        # System PM fallback
+        if test -n "$pm_pkg" -a -n "$pm"
+            echo "Updating $bin..."
+            _fish_deps_pm_upgrade $pm_pkg
+            set updated_any 1
+        end
+
+        set i (math $i + 1)
+    end
+
+    if test $updated_any -eq 0
+        echo "Nothing to update."
+    end
+end