fix(switch): extend NX-only asset prefix to audio and title/intro art

The previous NX gate only rewrote image paths that go through Assets.resolve.
Pokemon Yellow still had no sound and a blank title screen because:

- ChipSynth reads programs.bin directly via love.filesystem.read, bypassing
  Assets. On NX the unprefixed path is missing when the mount overlay fails,
  so the engine never built and every song/SFX was silent.
- Sound.playPikaCry loads pika_cries WAVs with love.audio.newSource, also
  bypassing Assets.resolve.
- TitleState, YellowIntro, and IntroMovie call love.graphics.newImage
  directly on unprefixed assets/generated paths, so the Pikachu title and
  intro atlases failed to load.

Fix: apply the same NX-only prefix rewrite in those four places.
Desktop/Android keep the existing mountVersion overlay behavior.

Also add ChipSynth._loadBanksForTest and tests covering the new paths.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/core/Sound.lua

@@ -269,6 +269,13 @@ function Sound.playPikaCry(data, n)
   if src == false then return nil end
   if not src then
     local path = ("assets/generated/audio/pika_cries/cry_%02d.wav"):format(n)
+    -- NX-only: Blue/Yellow live under a versioned save-dir prefix.
+    if require("src.core.Platform").isNX() then
+      local prefix = require("src.core.GameVersion").cachePrefix()
+      if prefix ~= "" and love.filesystem.getInfo(prefix .. path) then
+        path = prefix .. path
+      end
+    end
     local ok, s = pcall(love.audio.newSource, path, "static")
     if not ok or not s then
       cache[key] = false