feat: add i18n localization with language switcher to all web apps

- Add svelte-i18n configuration with SSR support to all web apps
- Create LanguageSelector component for each app with brand colors
- Add German and English locale files
- Integrate language switcher into login pages via headerControls snippet
- Fix Tailwind v4 @source directives for shared package scanning
- Update AppSlider styling to match login container design

Apps updated:
- Memoro (gold #f8d62b)
- Märchenzauber (pink #FF6B9D)
- ManaDeck (purple #8b5cf6)
- ManaCore (indigo #6366f1)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/shared-theme/package.json

@@ -3,14 +3,29 @@
   "version": "0.1.0",
   "private": true,
   "type": "module",
+  "svelte": "./src/index.ts",
   "main": "./src/index.ts",
   "types": "./src/index.ts",
   "exports": {
-    ".": "./src/index.ts",
-    "./store": "./src/store.svelte.ts",
-    "./types": "./src/types.ts",
-    "./constants": "./src/constants.ts",
-    "./utils": "./src/utils.ts"
+    ".": {
+      "svelte": "./src/index.ts",
+      "types": "./src/index.ts",
+      "default": "./src/index.ts"
+    },
+    "./store": {
+      "svelte": "./src/store.svelte.ts",
+      "default": "./src/store.svelte.ts"
+    },
+    "./types": {
+      "types": "./src/types.ts",
+      "default": "./src/types.ts"
+    },
+    "./constants": {
+      "default": "./src/constants.ts"
+    },
+    "./utils": {
+      "default": "./src/utils.ts"
+    }
   },
   "peerDependencies": {
     "svelte": "^5.0.0"