Sweep every machine for config worth tracking

Reactive capture missed wallust entirely, so this is a systematic pass over
~/.config on all four machines: every entry that is not already a symlink,
judged on whether it is hand-authored config or app-generated state.

Shared and identical everywhere -> common/: lazygit, ncmpcpp, neofetch,
matplotlib. Everything else differs per machine and goes in
hosts/<host>/config/: gtk-2.0/3.0/4.0, mimeapps.list, user-dirs.dirs,
mpv, swaync, swayimg, bob, pavucontrol.ini, zoom; plus beets, bottom,
glow and mpd on system76; fastfetch, gh, uv, traggo, tiling-assistant and
xdg-desktop-portal on the work laptop; inbox-tidy and llmfit on mainframe.

Deliberately excluded, all verified to hold live credentials: the work
laptop's Claude OAuth tokens (~/.config/anthropic/credentials), the NAS
restic repo password and hetzner.env, subsonic passwords in subtui, stmp
and termsonic, mopidy, supersonic, the Proton bridge env and the LiteLLM
virtual keys. The ignore list now names those shapes directly — a bare
`password` file would not have been caught before.

Also excluded as generated state or too large to be meaningful: GIMP,
kicad, BambuStudio, OrcaSlicer, calibre, LightBurn, obs-studio, feishin,
libreoffice, VirtualBox, FortiClient; and mainframe's dead X11-era
leftovers (i3, openbox, lxpanel, lxsession, pcmanfm).

hosts/sctfw004/config/user-dirs.dirs

@@ -0,0 +1,15 @@
+# This file is written by xdg-user-dirs-update
+# If you want to change or add directories, just edit the line you're
+# interested in. All local changes will be retained on the next run.
+# Format is XDG_xxx_DIR="$HOME/yyy", where yyy is a shell-escaped
+# homedir-relative path, or XDG_xxx_DIR="/yyy", where /yyy is an
+# absolute path. No other format is supported.
+# 
+XDG_DESKTOP_DIR="$HOME/"
+XDG_DOWNLOAD_DIR="$HOME/Downloads"
+XDG_TEMPLATES_DIR="$HOME/"
+XDG_PUBLICSHARE_DIR="$HOME/"
+XDG_DOCUMENTS_DIR="$HOME/"
+XDG_MUSIC_DIR="$HOME/"
+XDG_PICTURES_DIR="$HOME/"
+XDG_VIDEOS_DIR="$HOME/"