Standardise across machines; add genuinely-customised app config

Two passes, both aimed at a consistent experience rather than a faithful
snapshot of each machine's accidents.

Standardisation. Audited every host-layer config present on more than one
machine and asked whether the difference was intent or drift:
  - mpv was byte-identical; swayimg differed only because system76 still
    had the shipped default and the work laptop had the real config; bob
    differed by one setting the work laptop was simply missing.
  - user-dirs.dirs disagreed with BOTH machines and with zshenv, which has
    said $HOME/downloads all along. Standardised on that.
  - mimeapps.list is now the union of both machines' associations.
  - swaync's config and style are shared; only wallust's generated
    colors.css stays per host, alongside hypr's and waybar's.
All of the above moved to common/.

Dropped as pure state rather than config: gtk-2.0 (file-chooser geometry),
pavucontrol.ini (window size), zoom.conf (a per-install random_key) and
zoomus.conf (panel widths). gtk-3.0 stays per host — its bookmarks encode
the two different home directories.

App config. GIMP, inkscape, FreeCAD, cura, OrcaSlicer, LightBurn and OBS
all hold real settings, so a curated subset of each is now tracked:
settings, keybindings and user content, but not session state, tool
options, device lists or window geometry. kicad is skipped — both library
tables hold a single entry, i.e. untouched defaults.

Content lives once in common/ even when only one machine has the app; the
host configs decide who gets the link. That is the distinction that lets
53% of link sources be shared while the NAS still does not get GIMP.

Two exclusions on credential grounds: obs-studio/plugin_config holds a
websocket server_password, and gh is dropped entirely because `gh auth
login` writes a token into hosts.yml — now also blocked by name.

common/fastfetch/config.jsonc

@@ -0,0 +1,128 @@
+
+{
+"$schema": "https://github.com/fastfetch-cli/fastfetch/raw/dev/doc/json_schema.json",
+"logo": {
+"padding": {
+"top": 1
+}
+},
+"display": {
+"separator": " 󰑃  "
+},
+"modules": [
+    "break",
+    {
+    "type": "os",
+    "key": " DISTRO",
+    "keyColor": "yellow"
+    },
+    {
+    "type": "kernel",
+    "key": "│ ├",
+    "keyColor": "yellow"
+    },
+    {
+    "type": "packages",
+    "key": "│ ├󰏖",
+    "keyColor": "yellow"
+    },
+    {
+    "type": "shell",
+    "key": "│ └",
+    "keyColor": "yellow"
+    },
+    {
+    "type": "wm",
+    "key": " DE/WM",
+    "keyColor": "blue"
+    },
+    {
+    "type": "wmtheme",
+    "key": "│ ├󰉼",
+    "keyColor": "blue"
+    },
+    {
+    "type": "icons",
+    "key": "│ ├󰀻",
+    "keyColor": "blue"
+    },
+    {
+        "type": "cursor",
+        "key": "│ ├",
+        "keyColor": "blue",
+    },
+    {
+        "type": "terminalfont",
+        "key": "│ ├",
+        "keyColor": "blue",
+    },
+    {
+    "type": "terminal",
+    "key": "│ └",
+    "keyColor": "blue"
+    },
+    {
+    "type": "host",
+    "key": "󰌢 SYSTEM",
+    "keyColor": "green"
+    },
+    {
+    "type": "cpu",
+    "key": "│ ├󰻠",
+    "keyColor": "green"
+    },
+    {
+    "type": "gpu",
+    "key": "│ ├󰻑",
+    "format": "{2}",
+    "keyColor": "green"
+    },
+    {
+            "type": "display",
+    "key": "│ ├󰍹",
+    "keyColor": "green",
+    "compactType": "original-with-refresh-rate"
+    },
+    {
+    "type": "memory",
+    "key": "│ ├󰾆",
+    "keyColor": "green"
+    },
+    {
+    "type": "swap",
+    "key": "│ ├󰓡",
+    "keyColor": "green"
+    },
+    {
+    "type": "uptime",
+    "key": "│ ├󰅐",
+    "keyColor": "green"
+    },
+    {
+    "type": "display",
+    "key": "│ └󰍹",
+    "keyColor": "green"
+    },
+    {
+    "type": "sound",
+    "key": " AUDIO",
+    "format": "{2}",
+    "keyColor": "magenta"
+    },
+    {
+    "type": "player",
+    "key": "│ ├󰥠",
+    "keyColor": "magenta"
+    },
+    {
+    "type": "media",
+    "key": "│ └󰝚",
+    "keyColor": "magenta"
+    },
+    {
+    "type": "custom",
+    "format": "\u001b[90m  \u001b[31m  \u001b[32m  \u001b[33m  \u001b[34m  \u001b[35m  \u001b[36m  \u001b[37m  \u001b[38m  \u001b[39m  \u001b[39m    \u001b[38m  \u001b[37m  \u001b[36m  \u001b[35m  \u001b[34m  \u001b[33m  \u001b[32m  \u001b[31m  \u001b[90m "
+    },
+    "break",
+    ]
+}