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/Clipboard.qml

@@ -220,7 +220,7 @@ Singleton {
         }
 
         try {
-            root.entries = JSON.parse(text).map(row => root._normalise(row));
+            root.entries = JSON.parse(text).map(row => root._normalize(row));
         } catch (e) {
             console.warn("Clipboard: could not parse history —", e);
             root.entries = [];
@@ -231,7 +231,7 @@ Singleton {
 
     // Turn a raw row into what the UI actually asks questions of, so no
     // delegate has to know about column names or Vicinae's integer kinds.
-    function _normalise(row: var): var {
+    function _normalize(row: var): var {
         const encrypted = row.enc !== 0;
         const textual = row.kind === root.kindText || row.kind === root.kindLink;
         const raw = row.preview || "";