Offer to install PSP firmware updaters instead of running them

Opening an official updater (a PSP/GAME/UPDATE EBOOT.PBP, identified by the
MSTKUPDATE disc ID) from the main screen now brings up a confirmation dialog
that unpacks the firmware into the NAND directory, where the emulated
flash0/flash1 live. Running the updater itself doesn't work, so there was
nothing useful to do with one before.

Unpacks the file list for the model we claim to be (iPSPModel), on a worker
thread, with a progress bar - for which PSARUnpackOptions gets an optional
progress callback.

AGENTS.md: translate UI strings last, in a separate commit

The English string is what all ~47 languages get derived from, so rewording it
after the sweep means redoing the sweep. Check the wording first.

Co-Authored-By: Claude Opus 5 <[email protected]>

AGENTS.md

@@ -184,6 +184,11 @@ For string sanitation, we already have SanitizeString in StringUtils.cpp - add n
 
 ## Translated UI strings (assets/lang)
 
+**When implementing new UI, translations come last, in their own commit after everything else is
+done.** Write the English strings, get the feature built and working, commit that - then stop and ask
+the user to check the English wording before translating anything. The English string is what all ~47
+languages get derived from, so rewording it afterwards means redoing the whole sweep.
+
 One .ini file per language, keyed by section and key against `assets/lang/en_US.ini`. **Don't hand-edit
 the ~47 files**, and don't run the AI commands in `Tools/langtool` either - you can read the call site,
 which its fixed prompt can't. Do the translating yourself and let the tool do the file surgery. Run it