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/services/Displays.qml

@@ -141,7 +141,7 @@ Singleton {
                 ? persistedPrimaries[0].name
                 : (origin?.name ?? raw[0]?.name ?? "");
             root.monitors = raw.map(monitor => {
-                const modes = root.normaliseModes(monitor.availableModes ?? []);
+                const modes = root.normalizeModes(monitor.availableModes ?? []);
                 const width = monitor.width ?? 0;
                 const height = monitor.height ?? 0;
                 const refreshRate = monitor.refreshRate ?? 0;
@@ -200,7 +200,7 @@ Singleton {
     // resolution at distinct rates such as 60.00 and 59.94. Those identities
     // remain separate because confirmation and recovery must read back the
     // exact mode the user chose, even when their rounded labels look similar.
-    function normaliseModes(raw: var): var {
+    function normalizeModes(raw: var): var {
         const seen = {};
         const out = [];
         for (const entry of raw) {