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/App.svelte

@@ -21,6 +21,7 @@
   import ExplorerPanel from "./lib/components/ExplorerPanel.svelte";
   import FileHistoryPanel from "./lib/components/FileHistoryPanel.svelte";
   import GlobalSearchDialog from "./lib/components/GlobalSearchDialog.svelte";
+  import HelpOverlay from "./lib/components/HelpOverlay.svelte";
   import HistoryPanel from "./lib/components/HistoryPanel.svelte";
   import InteractiveRebaseDialog from "./lib/components/InteractiveRebaseDialog.svelte";
   import LinePatchDialog from "./lib/components/LinePatchDialog.svelte";
@@ -104,6 +105,7 @@
 
   import type {
     AiSettings,
+    AppLanguage,
     AppTheme,
     AnalyticsSettings,
     CommitAiPhase,
@@ -176,6 +178,7 @@
   const AI_SETTINGS_KEY = "gitlite.aiSettings.v1";
   const ANALYTICS_SETTINGS_KEY = "gitlite.analyticsSettings.v1";
   const APP_THEME_KEY = "gitlite.theme.v1";
+  const APP_LANGUAGE_KEY = "gitlite.language.v1";
   const COMMIT_PANEL_HEIGHT_KEY = "gitlite.commitPanelHeight.v1";
   const LEFT_SIDEBAR_WIDTH_KEY = "gitlite.leftSidebarWidth.v1";
   const LEFT_BRANCH_PANEL_HEIGHT_KEY = "gitlite.leftBranchPanelHeight.v1";
@@ -248,9 +251,11 @@
   let aiSettings: AiSettings = defaultAiSettings();
   let aiSettingsOpen = false;
   let appSettingsOpen = false;
+  let helpOpen = false;
   let analyticsNoticeOpen = false;
   let analyticsSettings: AnalyticsSettings = defaultAnalyticsSettings();
   let appTheme: AppTheme = loadThemePreference();
+  let appLanguage: AppLanguage = loadLanguagePreference();
   let localModelOptions: LocalModelOption[] = [];
   let errorMessage = "";
   let operation = "";
@@ -412,6 +417,7 @@
   $: allLeftPanelsCollapsed = branchPanelCollapsed && stashPanelCollapsed && explorerPanelCollapsed;
 
   $: applyThemePreference(appTheme);
+  $: applyLanguagePreference(appLanguage);
 
   // ── Lifecycle ──────────────────────────────────────────────────────────────
 
@@ -672,7 +678,7 @@
   }
 
   async function autoRefreshTick() {
-    if (!autoRefreshEnabled || activeView !== "repository" || !activeRepoPath || isBusy || autoRefreshInFlight || resolveDialogOpen || compareDialogOpen || compareSelectOpen || interactiveRebaseOpen || reflogOpen || newBranchCommit || globalSearchOpen) return;
+    if (!autoRefreshEnabled || activeView !== "repository" || !activeRepoPath || isBusy || autoRefreshInFlight || resolveDialogOpen || compareDialogOpen || compareSelectOpen || interactiveRebaseOpen || reflogOpen || newBranchCommit || globalSearchOpen || helpOpen) return;
     const path = activeRepoPath;
     autoRefreshInFlight = true;
     try {
@@ -813,6 +819,29 @@
     }
   }
 
+  function loadLanguagePreference(): AppLanguage {
+    try {
+      const stored = localStorage.getItem(APP_LANGUAGE_KEY);
+      if (stored === "en" || stored === "de") return stored;
+    } catch {
+      // Local storage is optional; English is the first-start default.
+    }
+    return "en";
+  }
+
+  function persistLanguagePreference(next: AppLanguage) {
+    try {
+      localStorage.setItem(APP_LANGUAGE_KEY, next);
+    } catch {
+      // Ignore storage quota/private-mode errors.
+    }
+  }
+
+  function applyLanguagePreference(next: AppLanguage) {
+    document.documentElement.lang = next;
+    document.documentElement.dataset.language = next;
+  }
+
   function applyThemePreference(next: AppTheme) {
     const prefersLight = themeMediaQuery?.matches ?? window.matchMedia("(prefers-color-scheme: light)").matches;
     const resolved = next === "system"
@@ -828,13 +857,15 @@
     if (appTheme === "system") applyThemePreference(appTheme);
   }
 
-  function saveAppSettings(next: AnalyticsSettings, nextTheme: AppTheme) {
+  function saveAppSettings(next: AnalyticsSettings, nextTheme: AppTheme, nextLanguage: AppLanguage) {
     analyticsSettings = next;
     appTheme = nextTheme;
+    appLanguage = nextLanguage;
     persistAnalyticsSettings(next);
     persistThemePreference(nextTheme);
+    persistLanguagePreference(nextLanguage);
     appSettingsOpen = false;
-    if (next.enabled) trackEvent("settings_saved", { analytics_enabled: 1, theme: nextTheme });
+    if (next.enabled) trackEvent("settings_saved", { analytics_enabled: 1, theme: nextTheme, language: nextLanguage });
   }
 
   function updateCommitMessage(message: string) {
@@ -3259,6 +3290,11 @@
     trackEvent("global_search_opened");
   }
 
+  function openHelp() {
+    helpOpen = true;
+    trackEvent("help_opened");
+  }
+
   async function compareSelectedCommits() {
     if (!canCompare) return;
     await runOperation("Comparing commits", async () => {
@@ -3449,6 +3485,15 @@
   // ── Event handlers ─────────────────────────────────────────────────────────
 
   function handleWindowKeydown(event: KeyboardEvent) {
+    if ((event.ctrlKey || event.metaKey) && event.key === "/") {
+      event.preventDefault();
+      openHelp();
+      return;
+    }
+    if (event.key === "Escape" && helpOpen) {
+      helpOpen = false;
+      return;
+    }
     if (event.key === "Escape" && repoTabContextMenu) closeRepoTabContextMenu();
     else if (event.key === "Escape" && pendingDiscard && !isBusy) closeDiscardConfirm();
     else if (event.key === "Escape" && compareDialogOpen) closeCompareDialog();
@@ -3499,6 +3544,8 @@
     onOpenInExplorer={openActiveRepoInExplorer}
     onToggleAutoRefresh={toggleAutoRefresh}
     onOpenSettings={() => { appSettingsOpen = true; }}
+    onOpenHelp={openHelp}
+    language={appLanguage}
   />
 
   <div class="shell-body">
@@ -4113,11 +4160,16 @@
   <AppSettingsDialog
     analytics={analyticsSettings}
     theme={appTheme}
+    language={appLanguage}
     onSave={saveAppSettings}
     onClose={() => { appSettingsOpen = false; }}
   />
 {/if}
 
+{#if helpOpen}
+  <HelpOverlay language={appLanguage} onClose={() => { helpOpen = false; }} />
+{/if}
+
 {#if linePatchOpen && linePatchFile}
   <LinePatchDialog
     file={linePatchFile}