fix(kon): float window sidebar, transcription doubling guard, branding

Float window fixes:
- Root layout now detects /float and /viewer URLs and hides Sidebar,
  Titlebar, TaskSidebar for secondary windows. Belt-and-braces fix
  since +layout@.svelte should handle this but may not in SPA mode.
- Float window title: "Ramble - To-do" → "Kon - To-do"

Transcription doubling guard:
- Added chunk_id deduplication set in DictationPage — if a chunk_id
  has already been processed, skip the duplicate result
- Set cleared on each new recording session

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

src/routes/float/+page.svelte

@@ -168,7 +168,7 @@
     data-tauri-drag-region
   >
     <span class="text-[12px] font-medium text-text-secondary tracking-wide" data-tauri-drag-region>
-      Ramble - To-do
+      Kon - To-do
     </span>
 
     <div class="flex-1" data-tauri-drag-region></div>