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/hypr/hyprlock.conf.template

@@ -3,9 +3,9 @@
 #
 # GENERATED FILE. Edit hyprlock.conf.template and re-run
 # quickshell/scripts/panama-theme-apps; editing this copy is overwritten on the
-# next colour scheme change.
+# next color scheme change.
 #
-# The colours here follow the desktop's light/dark setting. They used to be
+# The colors here follow the desktop's light/dark setting. They used to be
 # hardcoded Tokyo Night Moon, which meant the one screen you see most often
 # stayed dark when everything else went light.
 #