Show and remove installed game updates from the game info screen

An installed update silently replaces what the game boots, so the info
pane now says when there is one - version, size and where it lives - and
the context menu offers to remove it again.

Removing takes the whole PSP/GAME/<DISC_ID> folder when the update is all
that's in it. When a digital game shares the folder, only PBOOT.PBP goes,
since deleting the folder would take the game with it and nothing records
what the install wrote. The confirmation names the exact path either way.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_018izZ1mGTWhz2RqeudqsDQR

docs/pkg_notes.md

@@ -167,7 +167,7 @@ patch file are silently dropped, with no warning that anything was skipped.
 
 ## How PPSSPP handles them
 
-Three pieces, added 2026-08-21:
+Four pieces:
 
 - **`Core/Util/PkgUnpack.cpp`** reads a package: header, item table, both PARAM.SFOs, and the
   decryption. `PkgReader::Open()` gives you a `PkgInfo` with the disc ID, disc version and patch
@@ -177,6 +177,10 @@ Three pieces, added 2026-08-21:
   `InstallZipScreen` - it shows what the update patches, what it'll take up on disk, and where it's
   going. The size is exact rather than an estimate: package contents aren't compressed, so summing
   the item table is the answer. `GameManager::InstallPkgOnThread()` does the work.
+- **`GameScreen`** shows an installed update in the info pane, and offers "Delete Game Update" in
+  its context menu. Deleting takes the whole `PSP/GAME/<DISC_ID>` folder when the update is all
+  that's in it, and only `PBOOT.PBP` when a digital game shares the folder - nothing records what
+  an install wrote, so the executable is the only part still identifiable afterwards.
 - **`FindGameUpdatePBOOT()` in `Core/PSPLoaders.cpp`** is the boot-time half. Starting a disc looks
   for `ms0:/PSP/GAME/<DISC_ID>/PBOOT.PBP`, and boots that instead of `disc0:/PSP_GAME/SYSDIR/EBOOT.BIN`
   if it's there, leaving the disc mounted.