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

lvglh/lv_conf.h

@@ -30,8 +30,8 @@
 #define LV_LIMITS_INCLUDE       <limits.h>
 #define LV_STDARG_INCLUDE       <stdarg.h>
 
-/* Built-in memory pool: 256 KB should be plenty for our UI */
-#define LV_MEM_SIZE (256 * 1024U)
+/* Built-in memory pool: 1 MB for complex UI (file browser etc.) */
+#define LV_MEM_SIZE (1024 * 1024U)
 #define LV_MEM_POOL_EXPAND_SIZE 0
 #define LV_MEM_ADR 0