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, 3 insertions, 2 deletions

diff --git a/src/lib/Tools/ActivityHistory/Tool.svelte b/src/lib/Tools/ActivityHistory/Tool.svelte
index 3cf7b09e..5e84db9e 100644
--- a/src/lib/Tools/ActivityHistory/Tool.svelte
+++ b/src/lib/Tools/ActivityHistory/Tool.svelte
@@ -14,6 +14,7 @@ import ActivityHistoryGrid from "./Grid.svelte";
 import SettingHint from "$lib/Settings/SettingHint.svelte";
 import Skeleton from "$lib/Loading/Skeleton.svelte";
 import LogInRestricted from "$lib/Error/LogInRestricted.svelte";
+import locale from "$stores/locale";
 
 export let user: AniListAuthorisation;
 
@@ -99,10 +100,10 @@ const screenshot = async () => {
       <Spacer />
 
       <details open>
-        <summary>Days in risk of developing an activity history hole</summary>
+        <summary>{$locale().tools.activityHistory?.daysAtRisk}</summary>
 
         <SettingHint>
-          Days in which you did not log any activity or only have one activity logged.
+          {$locale().tools.activityHistory?.daysAtRiskHint}
         </SettingHint>
 
         <ul>