Validate save imports by main-data checksum, not raw file size

The SAVE FILES card only accepted saves of exactly 32768 bytes and
refused anything else. importToSlot now classifies a non-32768 file by
the integrity of its main-data checksum instead:

- Oversize + valid checksum -> an emulator RTC footer, so the launcher
  asks for confirmation, then truncates to 32768 on force.
- Oversize + invalid checksum -> rejected.
- Undersize + valid checksum -> imports zero-padded; otherwise refused.

Adds the "Oversized save file" confirm modal, a new vendor-oracle test
built by gen1lib (PKHeX-derived) run as its own Lua 5.4 tier, oversize/
truncated policy tests, and the LUA54 wiring in test.sh.

# Conflicts:
#	src/import/LauncherView.lua

src/save_convert/SaveConvert.lua

@@ -25,6 +25,7 @@ local GenSave = require("src.save_convert.GenSave")
 local SaveConvert = {}
 
 SaveConvert.SAVE_SIZE = GenSave.SAVE_SIZE
+SaveConvert.mainChecksumValid = GenSave.mainChecksumValid
 
 -- ------------------------------------------------------------------
 -- Crosswalk data loading (cached).  Mirrors src/core/Data.lua: prefer