feat(language): implement internationalization and help overlay

This update introduces comprehensive language support (English/German) across the application, enabling localization for UI elements and settings dialogs. It also adds a dedicated Help Overlay component with detailed guides on using Gitty's core Git features.

- Adds language selection to App Settings
- Implements German translations in key areas
- Introduces global help documentation accessible via Ctrl+/

src/lib/TitleBar.svelte

@@ -2,7 +2,7 @@
   import { onDestroy, onMount } from "svelte";
   import { getVersion } from "@tauri-apps/api/app";
   import { getCurrentWindow } from "@tauri-apps/api/window";
-  import { CloudDownload, Download, FolderOpen, GitBranch, GitCompare, History, ListRestart, LoaderCircle, Minus, RefreshCw, Search, Settings, Upload, X } from "@lucide/svelte";
+  import { CircleHelp, CloudDownload, Download, FolderOpen, GitBranch, GitCompare, History, ListRestart, LoaderCircle, Minus, RefreshCw, Search, Settings, Upload, X } from "@lucide/svelte";
   import iconUrl from "../../src-tauri/icons/icon.png";
 
   export let branch: string = "";
@@ -24,7 +24,9 @@
   export let onReflog: () => void = () => {};
   export let onOpenInExplorer: () => void = () => {};
   export let onToggleAutoRefresh: () => void = () => {};
+  export let onOpenHelp: () => void = () => {};
   export let onOpenSettings: () => void = () => {};
+  export let language: "en" | "de" = "en";
 
   let win: ReturnType<typeof getCurrentWindow> | null = null;
   let isMaximized = false;
@@ -238,14 +240,24 @@
         <span class="tb-action-label">Auto</span>
       </button>
 
+      <button
+        class="tb-action"
+        onclick={onOpenHelp}
+        title={language === "de" ? "Hilfe (Ctrl+/)" : "Help (Ctrl+/)"}
+        aria-label={language === "de" ? "Hilfe öffnen" : "Open help"}
+      >
+        <CircleHelp size={14} aria-hidden="true" />
+        <span class="tb-action-label">{language === "de" ? "Hilfe" : "Help"}</span>
+      </button>
+
       <button
         class="tb-action"
         onclick={onOpenSettings}
-        title="Settings"
-        aria-label="Settings"
+        title={language === "de" ? "Einstellungen" : "Settings"}
+        aria-label={language === "de" ? "Einstellungen" : "Settings"}
       >
         <Settings size={14} aria-hidden="true" />
-        <span class="tb-action-label">Settings</span>
+        <span class="tb-action-label">{language === "de" ? "Einstellungen" : "Settings"}</span>
       </button>
     </div>