Preserve.ini for update cleanup, Hekate UI strings, docs

- Load sd:/config/omninx/preserve.ini during update mode cleanup to skip
  delete paths that overlap user-preserved prefixes (heap-backed path list).
- Document preserve.ini in PRESERVE_INI.md, README, and INSTALLATION_PROCESS.
- Prefer Hekate wording in main.c user messages for bootloader launch/errors.
- Extend update deletion list for exefs_patches (audio_mastervolume, SaltyNX_Fixes, logo).

source/install.h

@@ -32,6 +32,9 @@ int clean_mode_wipe(void);
 int clean_mode_restore(void);
 int clean_mode_install(omninx_variant_t variant);
 
+void install_preserve_update_cleanup_begin(void);
+void install_preserve_update_cleanup_end(void);
+
 // Shared helpers (install.c) - used by install_update.c and install_clean.c
 void install_set_color(u32 color);
 void install_check_and_clear_screen_if_needed(void);