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/obs-studio/global.ini

@@ -0,0 +1,72 @@
+[General]
+Pre19Defaults=false
+Pre21Defaults=false
+Pre23Defaults=false
+Pre24.1Defaults=false
+MaxLogs=10
+InfoIncrement=-1
+ProcessPriority=Normal
+EnableAutoUpdates=true
+ConfirmOnExit=true
+HotkeyFocusType=NeverDisableHotkeys
+FirstRun=true
+LastVersion=536870914
+Pre31Migrated=true
+BrowserHWAccel=true
+
+[Video]
+Renderer=OpenGL
+
+[BasicWindow]
+PreviewEnabled=true
+PreviewProgramMode=false
+SceneDuplicationMode=true
+SwapScenesMode=true
+SnappingEnabled=true
+ScreenSnapping=true
+SourceSnapping=true
+CenterSnapping=false
+SnapDistance=10
+SpacingHelpersEnabled=true
+RecordWhenStreaming=false
+KeepRecordingWhenStreamStops=false
+SysTrayEnabled=true
+SysTrayWhenStarted=false
+SaveProjectors=false
+ShowTransitions=true
+ShowListboxToolbars=true
+ShowStatusBar=true
+ShowSourceIcons=true
+ShowContextToolbars=true
+StudioModeLabels=true
+VerticalVolControl=false
+MultiviewMouseSwitch=true
+MultiviewDrawNames=true
+MultiviewDrawAreas=true
+MediaControlsCountdownTimer=true
+geometry=AdnQywADAAAAAAoAAAAAAAAAE/kAAAV2AAAKAAAAAAAAABP5AAAFdgAAAAEAAAAACgAAAAoAAAAAAAAAE/kAAAV2
+DockState=AAAA/wAAAAD9AAAAAQAAAAMAAAn6AAAA2PwBAAAABvsAAAAUAHMAYwBlAG4AZQBzAEQAbwBjAGsBAAAAAAAAAfwAAACYAP////sAAAAWAHMAbwB1AHIAYwBlAHMARABvAGMAawEAAAIAAAAB+wAAAJgA////+wAAABIAbQBpAHgAZQByAEQAbwBjAGsBAAAD/wAAApIAAADeAP////sAAAAeAHQAcgBhAG4AcwBpAHQAaQBvAG4AcwBEAG8AYwBrAQAABpUAAAGGAAAApQD////7AAAAGABjAG8AbgB0AHIAbwBsAHMARABvAGMAawEAAAgfAAAB2wAAAKIA////+wAAABIAcwB0AGEAdABzAEQAbwBjAGsCAAADogAAAmwAAAK8AAAAyAAACfoAAARiAAAABAAAAAQAAAAIAAAACPwAAAAA
+AlwaysOnTop=false
+EditPropertiesMode=false
+DocksLocked=false
+SideDocks=false
+
+[Basic]
+Profile=Untitled
+ProfileDir=Untitled
+SceneCollection=Untitled
+SceneCollectionFile=Untitled
+ConfigOnNewProfile=true
+
+[PropertiesWindow]
+cx=1173
+cy=1368
+
+[ScriptLogWindow]
+geometry=AdnQywADAAAAAAoBAAAAGQAADFgAAAGoAAAKAQAAABkAAAxYAAABqAAAAAEAAAAACgAAAAoBAAAAGQAADFgAAAGo
+
+[Locations]
+Configuration=/home/connor/.config
+SceneCollections=/home/connor/.config
+Profiles=/home/connor/.config
+PluginManagerSettings=/home/connor/.config