docs: answer gallery media and exFAT names

The start pages are at their word ceilings: the two answers move to the technical FAQ, and the testing guide names test_install_filesystems.

wiki/faq.md

@@ -101,11 +101,6 @@ Fill it from a computer or point `--from-pack` at your ZIP: [Without a network](
 `--from` copies BIOS files from an old card or backup:
 [Copy from an old card](installer.md#copy-from-an-old-card).
 
-## BIOS pictures or sounds in my phone's gallery?
-
-An empty file named `.nomedia` in the BIOS folder hides them. The installer
-adds it on Android: [Android](installer.md#android).
-
 ## My setup is not in the list
 
 - Name your emulator's BIOS folder with `--dest`.

wiki/technical-faq.md

@@ -169,6 +169,22 @@ Running `verify.py --emulator <core> --verbose` shows the emulator-level ground
 
 It reaches only as far as the profiles do. Files no profile states a value for are platform-only, and nothing can be said about their content. The footer of the platform report gives that ratio as `Ground truth: N/M files have emulator validation`.
 
+## Why do BIOS pictures and sounds show in my phone's gallery?
+
+Android's media scanner indexes every image, sound and video in shared
+storage, and the RetroArch BIOS folder holds 3,842 of them (FBNeo samples,
+overlays, PPSSPP assets, sdlpal's videos). An empty file named `.nomedia` in
+the BIOS folder hides it and every folder below it. The installer writes one
+on Android and the RetroArch pack carries one: see [Android](installer.md#android).
+Copied by hand without either, create the empty file yourself.
+
+## Why were files left out on my exFAT card?
+
+FAT, exFAT and Windows refuse `< > : " | ? *` in a name, and RetroDECK's list
+names three files with a colon, like `zxs:48.rom`. The installer leaves those
+out on such a card and names them. An ext4 card holds them. See
+[Upper and lower case](installer.md#upper-and-lower-case).
+
 ## Next steps
 
 - [Reference](index.md), every reference page in one list

wiki/testing-guide.md

@@ -59,7 +59,7 @@ Every module in `tests/`, by the area it guards.
 | Packs and manifests | synthetic + real packs | `test_artifact_lock`, `test_atomic_artifacts`, `test_batocera_cores`, `test_core_data_trees`, `test_deterministic_zip`, `test_emulator_pack_counts`, `test_finalize_pack_names`, `test_large_file_cache`, `test_libretro_layout`, `test_manifest_entry`, `test_minui_platform`, `test_no_game_data`, `test_pack_conformance_dirs`, `test_pack_core_extras`, `test_pack_counts`, `test_pack_destinations`, `test_pack_failures`, `test_pack_file_names`, `test_pack_grouping`, `test_pack_integrity`, `test_pack_member_identity`, `test_pack_readme`, `test_platform_inheritance`, `test_platform_keys`, `test_release_packs`, `test_required_only_archives`, `test_required_only_twins`, `test_save_root`, `test_split_extras`, `test_split_names`, `test_split_pack`, `test_system_pack_extras`, `test_system_pack_parity`, `test_torrentzip`, `test_which_pack` |
 | Slots and regions | synthetic + profiles | `test_region`, `test_region_agnostic_scan`, `test_region_groups`, `test_region_held`, `test_region_platform_index`, `test_region_required_only`, `test_slot`, `test_slots`, `test_slots_shipped_file` |
 | Hardware targets and systems | synthetic + target files | `test_amberelec_targets`, `test_emuelec_targets`, `test_extract_targets`, `test_lakka_targets`, `test_libretro_slugs`, `test_system_ids`, `test_system_selection`, `test_target_names`, `test_target_scrapers`, `test_target_systems`, `test_target_verify` |
-| Installer and downloads | loopback server | `test_check_release`, `test_download`, `test_install`, `test_install_cores`, `test_install_experience`, `test_install_app`, `test_install_from`, `test_install_games`, `test_install_offline`, `test_install_selection`, `test_install_tui` |
+| Installer and downloads | loopback server | `test_check_release`, `test_download`, `test_install`, `test_install_cores`, `test_install_experience`, `test_install_filesystems`, `test_install_app`, `test_install_from`, `test_install_games`, `test_install_offline`, `test_install_selection`, `test_install_tui` |
 | Handheld launchers | a pty as the console, fake installer and firmware tools, stubbed PortMaster dialogs | `test_handheld_launchers`, `test_port` |
 | Running cores | parsers on fixed inputs, a libretro core built from C in the test when a compiler exists | `test_core_probe` |
 | Measurement records | synthetic record files, the committed `measurements/` against HEAD, the **Proof** line naming the BIOS a core ran, and that no page shows a Tested block, a region outcome or a time per frame | `test_measurements` |

wiki/troubleshooting.md

@@ -50,8 +50,6 @@ Without `--check`, it adds missing files and replaces wrong ones.
   folder. Emulators add their own, like `dc/` for Flycast.
 - **A ZIP in parts, like `Pack.part1of2.zip`?** Unzip all parts into one
   folder.
-- **"left out" on an exFAT card?** The card refuses a `:` in a name. An
-  ext4 card holds these files.
 
 <!-- Flycast's libretro port appends "dc/" to the system directory:
 shell/libretro/libretro.cpp:2252-2253, emulators/flycast.yml. -->