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

docs/superpowers/specs/2026-08-17-panama-cohesion-design.md

@@ -55,7 +55,7 @@ $ hyprctl getoption decoration:rounding -j                      →  "int": 4
 `eval` is also strictly more capable than `keyword` — it can set *any* config
 value, including gradients, animation curves, and nested tables. It executes
 arbitrary Lua, so the existing "never interpolate UI text into a command" rule
-must extend to it: values are validated and serialised numerically, never
+must extend to it: values are validated and serialized numerically, never
 concatenated from user input.
 
 ### Finding 2: three disconnected sources of truth for the same three values
@@ -206,7 +206,7 @@ promote the ~40 hardcoded `Settings.qml` values into real controls, and give
 Appearance genuine content: accent pair, window rounding, gaps, border size,
 blur, animation speed, bar height, font scale, and wallpaper.
 
-Appearance customisation stays inside the design language. The user picks how much
+Appearance customization stays inside the design language. The user picks how much
 of it there is — spacing, softness, motion — not a free-form palette editor that
 would let the Prism identity be dismantled by accident.
 
@@ -223,13 +223,13 @@ defaults, and Settings applies them live with `hyprctl eval`.
 
 - No UI-supplied string is ever interpolated into an `eval`, a shell command, or
   a config value. Numbers are range-checked; choices are matched against an
-  allow-list; colours are validated as hex before serialisation.
+  allow-list; colors are validated as hex before serialization.
 - A malformed or absent `settings.json` must degrade to shipped defaults, never
   to a broken compositor.
 - `hyprctl keyword` is banned in this codebase. It exits 0 without acting.
 - Every write path must be observably verified — read the value back rather than
   trusting an exit code. Finding 1 exists because an exit code was trusted.
-- Tokyo Night Moon and Prism remain the only visual identity. Customisation
+- Tokyo Night Moon and Prism remain the only visual identity. Customization
   adjusts its parameters, it does not replace it.
 - Motion stays event-driven. No idle repaint, at any setting.
 - GNOME keeps ownership of hardware, accounts, printers, and users.