feat: file dispatch system, file-type icons, multi-instance notepad

- Add extension-based dispatch to driver.storage.filedispatch with typed
  union (variant record THandlerKind = hkMagic/hkExtension)
- Extract file-type icon constants and mapping to core.gfx.fileicons
- Add core.search utility (getFileExtension, fmtFileSize, sortStringArray)
- Generate PUA bitmap icon fonts (32/64/128px) from Font Awesome via
  gen_file_icons.py + compile_icons.sh toolchain
- Integrate file dispatch into file browser (double-click triggers dispatch)
- Register notepad as handler for text file extensions
- Fix init order in app.mgr (filedispatch.init before app inits)
- Refactor notepad from singleton to multi-instance (up to 8 windows)
  using instance array, findStateByWid, and LVGL user_data on msgboxes

src/svc/svc.gfxd.pas

@@ -54,10 +54,12 @@ begin
         should_update := should_update or (CURRENT_TICK < LAST_UPDATE);  { handle tick counter wraparound }
         if (should_update) then begin
             LAST_UPDATE := CURRENT_TICK;
+            lvgl_lock;
             driver.video.windows.reapOrphanedWindows;
             driver.video.desktop.update;
             app.uidebug.update;
             lvgl_handler;
+            lvgl_unlock;
             driver.video.Flush;
         end;
         if SHOULD_CRASH then begin