refactor(locale): move hardcoded UI strings into english locale

Adds optional namespaces (common, errors, commandPalette, headTitle,
notifications, schedule, events, home, reader, routes, badgePreview,
badgeWall) and extends existing ones (settings.*, lists.*, tools.*,
user.*, hololive.*) on the Locale interface. New fields are optional
so japanese.ts can omit them; svelte-i18n's fallbackLocale handles
the runtime miss.

HeadTitle gains an optional routeKey prop for type-safe lookup.
defaultActions becomes a factory so the command palette re-reads
locale on language toggle. The existing JP feedback translation
in routes/settings is preserved via japanese.ts.

Out of scope (kept hardcoded): service-worker.ts, app.html,
Landing*.svelte, tools.ts registry, Easter Event 2025 pages.

1 files changed, 18 insertions, 3 deletions

diff --git a/src/lib/Home/HeadTitle.svelte b/src/lib/Home/HeadTitle.svelte
index 0759943f..73cf3e3d 100644
--- a/src/lib/Home/HeadTitle.svelte
+++ b/src/lib/Home/HeadTitle.svelte
@@ -1,9 +1,24 @@
 <script lang="ts">
 import { siteUrl } from "$lib/Utility/appOrigin";
+import locale from "$stores/locale";
+import type { Locale } from "$lib/Locale/layout";
 
-let { route = undefined, path = "/" }: { route?: string; path?: string } =
-	$props();
-const title = $derived((route ? `${route} • ` : "") + "due.moe");
+type HeadTitleKey = keyof NonNullable<Locale["headTitle"]>;
+
+let {
+	route = undefined,
+	routeKey = undefined,
+	path = "/",
+}: {
+	route?: string;
+	routeKey?: HeadTitleKey;
+	path?: string;
+} = $props();
+
+const resolved = $derived(
+	routeKey ? ($locale().headTitle?.[routeKey] ?? routeKey) : route,
+);
+const title = $derived((resolved ? `${resolved} • ` : "") + "due.moe");
 </script>
 
 <svelte:head>