Convert British spellings to American across the repo

colour -> color, behaviour -> behavior, centre -> center, favourite ->
favorite, and about twenty other pairs, applied consistently across
comments, docs, error/UI copy, and a handful of QML identifiers that
used the British spelling as their actual name: SystemSettings'
serialiseValue/serialiseTable/normaliseGradient, Displays'
normaliseModes, Wallpaper's normalisePolicy, SettingsBackup's
serialiseHomeState, DateTime's ntpSynchronised property, Clipboard's
_normalise helper, and ShortcutCapture's cancelled signal (with its
onCancelled handler in ShortcutsPage.qml). Every call site and the two
tests that assert on the literal source text (settings-ownership and
settings-backup-live contracts) were updated in lockstep.

Left untouched: config/dot/espanso/match/packages/misspell-en/ is a
vendored third-party autocorrect dictionary -- its entries are typo
corrections, not our prose, and rewriting them would fight the
package's own purpose (and any future re-sync from upstream).

The already-American `favorites` property (Home page pinned
accessories) was never actually misspelled -- only nearby comments and
error strings said "favourites" -- so no data migration was needed
there.

Claude-Session: https://claude.ai/code/session_01E6TJUAh41HaP25MVHWkhRZ

config/dot/quickshell/modules/settings/ShortcutsPage.qml

@@ -7,7 +7,7 @@
 // description in hypr/keybinds.lua, and this page just groups and renders them.
 //
 // The hardware settings above the list are real controls. Keyboard layout,
-// repeat behaviour, and pointer response are Hyprland's, so Panama owns them;
+// repeat behavior, and pointer response are Hyprland's, so Panama owns them;
 // device-specific configuration stays with GNOME.
 
 import QtQuick
@@ -174,7 +174,7 @@ SettingsPage {
                                 Keybinds.rebind(bindRow.modelData.luaChord, chord);
                                 root.capturingChord = "";
                             }
-                            onCancelled: root.capturingChord = ""
+                            onCanceled: root.capturingChord = ""
                         }
 
                         Row {