feat: i18n seam — typed t() + en dictionary

Nav and header wired as proof. Full string extraction deferred until a
second locale exists; CONTRIBUTING records the convention.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/frontend/src/App.tsx

@@ -18,6 +18,7 @@ import { StatusPagesPage } from "@/pages/StatusPagesPage";
 import { StatusPublicPage } from "@/pages/StatusPublicPage";
 import { Button } from "@/components/ui/button";
 import { cn } from "@/lib/utils";
+import { t, type Key } from "@/i18n";
 import type { Item } from "@/types";
 
 export default function App() {
@@ -28,13 +29,13 @@ export default function App() {
 	);
 }
 
-const NAV = [
-	{ href: "/", label: "Board", icon: LayoutGrid },
-	{ href: "/monitors", label: "Monitors", icon: Activity },
-	{ href: "/domains", label: "Domains", icon: Globe },
-	{ href: "/systems", label: "Systems", icon: Server },
-	{ href: "/incidents", label: "Incidents", icon: AlertTriangle },
-	{ href: "/status", label: "Status", icon: Megaphone },
+const NAV: { href: string; labelKey: Key; icon: typeof LayoutGrid }[] = [
+	{ href: "/", labelKey: "nav.board", icon: LayoutGrid },
+	{ href: "/monitors", labelKey: "nav.monitors", icon: Activity },
+	{ href: "/domains", labelKey: "nav.domains", icon: Globe },
+	{ href: "/systems", labelKey: "nav.systems", icon: Server },
+	{ href: "/incidents", labelKey: "nav.incidents", icon: AlertTriangle },
+	{ href: "/status", labelKey: "nav.status", icon: Megaphone },
 ];
 
 function Shell() {
@@ -94,14 +95,14 @@ function Shell() {
 								)}
 							>
 								<n.icon size={13} strokeWidth={1.8} />
-								{n.label}
+								{t(n.labelKey)}
 							</Link>
 						);
 					})}
 				</nav>
 				<div className="ml-auto flex items-center gap-2">
 					<Button
-						variant="outline" aria-label="Search (⌘K)"
+						variant="outline" aria-label={t("header.search")}
 						onClick={() => setPaletteOpen(true)}
 						className="gap-1.5 text-text-faint"
 					>
@@ -109,27 +110,27 @@ function Shell() {
 						<kbd className="hidden font-mono text-[10px] min-[620px]:inline">⌘K</kbd>
 					</Button>
 					<Button
-						variant="outline" size="icon" aria-label="Settings"
+						variant="outline" size="icon" aria-label={t("header.settings")}
 						onClick={() => setSettingsOpen(true)}
 					>
 						<Settings size={15} strokeWidth={1.8} />
 					</Button>
 					<Button
-						variant="outline" size="icon" aria-label="Toggle theme"
+						variant="outline" size="icon" aria-label={t("header.theme")}
 						onClick={() => void board.setSetting("theme", board.theme === "dark" ? "light" : "dark")}
 					>
 						{board.theme === "dark" ? <Moon size={15} strokeWidth={1.8} /> : <Sun size={15} strokeWidth={1.8} />}
 					</Button>
 					<Button
-						variant="outline" aria-label="Add widget"
+						variant="outline" aria-label={t("header.addWidget")}
 						onClick={() => { setEditing(undefined); setWdgOpen(true); }}
 					>
 						<LayoutGrid size={13} strokeWidth={2} />
-						Widget
+						{t("header.widget")}
 					</Button>
 					<Button onClick={() => { setEditing(undefined); setSvcOpen(true); }}>
 						<Plus size={13} strokeWidth={2.2} />
-						Add service
+						{t("header.addService")}
 					</Button>
 				</div>
 			</header>

apps/frontend/src/i18n/en.ts

@@ -0,0 +1,27 @@
+// English source strings. Flat keys, dot-separated namespaces.
+// Add a locale by copying this file — keys must match exactly.
+export const en = {
+	"nav.board": "Board",
+	"nav.monitors": "Monitors",
+	"nav.domains": "Domains",
+	"nav.systems": "Systems",
+	"nav.incidents": "Incidents",
+	"nav.status": "Status",
+
+	"header.search": "Search (⌘K)",
+	"header.settings": "Settings",
+	"header.theme": "Toggle theme",
+	"header.addWidget": "Add widget",
+	"header.addService": "Add service",
+	"header.widget": "Widget",
+
+	"common.add": "Add",
+	"common.edit": "Edit",
+	"common.delete": "Delete",
+	"common.cancel": "Cancel",
+	"common.save": "Save",
+	"common.test": "Test",
+	"common.loading": "Loading…",
+} as const;
+
+export type Key = keyof typeof en;

apps/frontend/src/i18n/index.ts

@@ -0,0 +1,13 @@
+import { en, type Key } from "@/i18n/en";
+
+export type { Key } from "@/i18n/en";
+
+// i18n seam: dictionaries are plain objects keyed by dotted names. `t` is a
+// typed lookup that falls back to the key itself, so a missing translation
+// renders the key — loud in dev, never a crash. Locales beyond `en` plug in
+// here later (settings key + lazy import); nothing else changes.
+const dict: Record<Key, string> = en;
+
+export function t(key: Key): string {
+	return dict[key] ?? key;
+}