feat(kon): replace browser clipboard with arboard

- New copy_to_clipboard Tauri command using arboard 3.6
- Replaced all 5 navigator.clipboard.writeText() calls across
  DictationPage, HistoryPage, FilesPage, and viewer with invoke()
- Native clipboard access independent of WebView permissions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/routes/viewer/+page.svelte

@@ -1,7 +1,7 @@
 <script>
   import { onMount, onDestroy } from "svelte";
   import { getCurrentWindow } from "@tauri-apps/api/window";
-  import { convertFileSrc } from "@tauri-apps/api/core";
+  import { convertFileSrc, invoke } from "@tauri-apps/api/core";
   import { formatTime, formatDuration } from "$lib/utils/time.js";
   import { PLAYBACK_SPEEDS } from "$lib/utils/constants.js";
 
@@ -193,7 +193,7 @@
 
   function copySegment(idx) {
     if (item?.segments?.[idx]) {
-      navigator.clipboard.writeText(item.segments[idx].text.trim()).catch(() => {});
+      invoke("copy_to_clipboard", { text: item.segments[idx].text.trim() }).catch(() => {});
     }
   }