feat(cli): replace the classic coreutils tools with modern equivalents

Adds Rust/Go replacements for the day-to-day utilities and shadows four of
them with aliases. Only read-only commands are shadowed (cat, du, df, ps), so a
wrong flag costs a retype rather than data; rm, grep, find and sed keep their
originals and the replacements are reached by their own names.

The aliases land in .zshrc, so they apply to interactive zsh only -- scripts,
`sudo <cmd>` and anything exec'd by another program still get the real binary.

New on every host: dust, dysk, procs, trash-cli, doggo, xh, ouch, jnv, hexyl,
fq and tealdeer. dysk is used rather than duf, which is unmaintained upstream.

git gains difftastic behind a `git dft` alias. diff.external is deliberately
left unset so delta remains the renderer for git diff/show and for anything
parsing them.

The work box gains kubecolor, aliased over kubectl; it wraps the real kubectl
and drops colour when stdout is not a terminal, so pipes are unchanged.

home/README.md documents the alias map, the flag incompatibilities (including
the two that fail silently: dust -s is --apparent-size, and procs reads a bare
`aux` as a search keyword) and the rationale for what was left alone.

home/shell.nix

@@ -26,8 +26,32 @@ in
     pkgs.tea
     pkgs.hyperfine # command-line benchmarking
     pkgs.sd # saner find-and-replace than sed
+
+    # Replacements for the classic coreutils/BSD tools. Only the read-only ones
+    # are aliased over the original name (see shellAliases below); the rest keep
+    # their own name so nothing changes shape under a script's feet. The alias
+    # map and the flag-compatibility differences are documented in
+    # ./README.md, "Replacing the classics".
+    pkgs.dust # du: tree-shaped, size-sorted disk usage
+    pkgs.dysk # df: mounted filesystems (duf is unmaintained upstream)
+    pkgs.procs # ps: process list with tree, ports and container columns
+    pkgs.trash-cli # rm: XDG trash; `trash` / `trash-list` / `trash-restore`
+    pkgs.doggo # dig: DNS lookups
+    pkgs.xh # curl, for interactive HTTP poking (curl stays for scripts)
+    pkgs.ouch # tar/unzip/7z/zstd: one command for every archive format
+    pkgs.jnv # interactive jq filter builder (jq itself stays for scripts)
+    pkgs.hexyl # hex viewer
+    pkgs.fq # jq for binary formats
   ];
 
+  # tldr pages: worked examples for a command, next to (not instead of) man.
+  # enableAutoUpdates defaults on and installs a tldr-update user timer, which
+  # keeps the page cache fresh -- without it `tldr` fails until first `--update`.
+  programs.tealdeer = {
+    enable = true;
+    settings.display.compact = true;
+  };
+
   # Resource monitor, themed Catppuccin Mocha to match the rest of the desktop.
   # btop does not bundle the theme, so vendor it from catppuccin/btop (pinned).
   programs.btop = {
@@ -137,6 +161,26 @@ in
       la = "eza --icons --git -la";
       lt = "eza --icons --git --tree";
       cls = "clear";
+
+      # Shadow the classics with their modern equivalents. Only read-only
+      # commands are shadowed: a wrong flag costs a retype, never data. The
+      # flag vocabularies are NOT compatible (`du -sh`, `df -h`, `ps aux` all
+      # fail here) -- see ./README.md, "Replacing the classics".
+      #
+      # Blast radius is bounded by where these live: shellAliases lands in
+      # .zshrc, so only interactive zsh sees them. Scripts, `sudo <cmd>` and
+      # anything exec'd by another program still get the real binary. To reach
+      # the original in an interactive shell: `command du` or `\du`.
+      cat = "bat --paging=never"; # bat is already the PAGER/MANPAGER
+      du = "dust";
+      df = "dysk";
+      ps = "procs";
+
+      # `rm` is deliberately NOT aliased to trash-put. Retraining `rm` to mean
+      # "recoverable" is a habit that follows you onto machines where it does
+      # not (every remote host, every root shell, every container), and trash
+      # semantics break down anyway on a different filesystem or on
+      # root-owned paths. Type `trash` when you want a trash can.
     };
   };