feat(i18n): install react-i18next, create English locale files, and initialize i18n framework

- Install i18next, react-i18next, i18next-browser-languagedetector
- Create 6 namespace JSON files (common, collection, threads, setups, onboarding, settings)
- Initialize i18n with language detection (localStorage + navigator)
- Wire i18n import in main.tsx before React rendering

Phase 34, Plan 01

src/client/locales/en/settings.json

@@ -0,0 +1,32 @@
+{
+	"title": "Settings",
+	"language": {
+		"title": "Language",
+		"description": "Change the display language of the app"
+	},
+	"weightUnit": {
+		"title": "Weight Unit",
+		"description": "Choose the unit used to display weights across the app"
+	},
+	"currency": {
+		"title": "Currency",
+		"description": "Changes the currency symbol displayed. This does not convert values."
+	},
+	"apiKeys": {
+		"title": "API Keys",
+		"description": "API keys allow programmatic access to GearBox (e.g., from Claude Desktop or scripts).",
+		"copyWarning": "Copy this key now — it won't be shown again:",
+		"namePlaceholder": "Key name (e.g., claude-desktop)"
+	},
+	"importExport": {
+		"title": "Import / Export",
+		"description": "Export your gear collection as a CSV file, or import items from a CSV.",
+		"export": "Export CSV",
+		"import": "Import CSV",
+		"importing": "Importing...",
+		"imported": "{{count}} items imported.",
+		"imported_one": "{{count}} item imported.",
+		"newCategories": "New categories: {{categories}}",
+		"noItemsFound": "No items found in the CSV."
+	}
+}