fix(switch): centralize the NX asset fallback in a boot-time loader overlay

The scattered per-call-site prefix rewrites were a parallel track that any
future newImage("assets/generated/...") would silently bypass.  Replace
them with NxAssetOverlay: installed once from love.load on NX only, it
wraps newImage / newImageData / newSource / filesystem.read / getInfo so a
missing assets/generated path falls back to the active version's
blue|yellow copy.  Call sites return to plain love loader calls, and
Assets.resolve goes back to being the platform-free mod-override point.

Two deliberate exceptions remain: the chip-audio worker (separate Lua
state) keeps receiving the prefix explicitly via audio.programPrefix, and
data/generated module loads keep using CacheFs.readActive.

A new guard test (tests/engine/nx_generated_guard_test.lua) fails CI on
any direct love loader call with a literal assets/generated path, so the
class of bug cannot regress by accident.  scripts/test.sh --quick is
green across all tiers.

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

src/ui/IntroMovie.lua

@@ -136,7 +136,7 @@ local FIGHT_SCRIPT = {
 
 local function tryImage(path)
   if not path then return nil end
-  local ok, img = pcall(love.graphics.newImage, require("src.render.Assets").resolve(path))
+  local ok, img = pcall(love.graphics.newImage, path)
   return ok and img or nil
 end
 

src/ui/SurfingMinigame.lua

@@ -92,7 +92,7 @@ function SurfingMinigame.new(game, onDone)
   self.banner = nil       -- {quad, frames}: GOOD!/YEAH-/Oh no..
 
   local function sheet(path)
-    local ok, img = pcall(love.graphics.newImage, require("src.render.Assets").resolve(path))
+    local ok, img = pcall(love.graphics.newImage, path)
     return ok and img or nil
   end
   self.bg = sheet("assets/generated/minigame/surf_1a.png")

src/ui/TitleState.lua

@@ -100,7 +100,7 @@ local CYCLE_FRAMES = 240 -- the original waits ~4s between picks
 
 local function tryImage(path)
   if not path then return nil end
-  local ok, img = pcall(love.graphics.newImage, require("src.render.Assets").resolve(path))
+  local ok, img = pcall(love.graphics.newImage, path)
   return ok and img or nil
 end
 

src/ui/TownMap.lua

@@ -104,7 +104,7 @@ local function loadBackground(game)
   local tm = (game.data.field or {}).townMap or {}
   local bg = tm.background
   if not (bg and bg.map and bg.tiles) then return nil end
-  local ok, img = pcall(love.graphics.newImage, require("src.render.Assets").resolve(bg.tiles.path))
+  local ok, img = pcall(love.graphics.newImage, bg.tiles.path)
   if not ok then return nil end
   local quads = {}
   local iw, ih = img:getDimensions()
@@ -115,7 +115,7 @@ local function loadBackground(game)
   end
   local cursor
   if bg.cursor then
-    local okc, c = pcall(love.graphics.newImage, require("src.render.Assets").resolve(bg.cursor.path))
+    local okc, c = pcall(love.graphics.newImage, bg.cursor.path)
     cursor = okc and c or nil
   end
   return { img = img, quads = quads, map = bg.map, cursor = cursor }
@@ -192,9 +192,8 @@ function TownMap.new(game, opts)
     -- field.townMap.nest lifts the icon path out of the engine
     local nest = ((game.data.field or {}).townMap or {}).nest
     local ok, img = pcall(love.graphics.newImage,
-                          require("src.render.Assets").resolve(
-                            (nest and nest.path)
-                            or "assets/generated/townmap/nest.png"))
+                          (nest and nest.path)
+                          or "assets/generated/townmap/nest.png")
     self.nestIcon = ok and img or nil
   end
   if opts.fly then

src/ui/TradeAnim.lua

@@ -29,7 +29,7 @@ local DEFAULT_ART = {
 
 local function tryImage(path)
   if not path then return nil end
-  local ok, img = pcall(love.graphics.newImage, require("src.render.Assets").resolve(path))
+  local ok, img = pcall(love.graphics.newImage, path)
   return ok and img or nil
 end
 

src/ui/YellowIntro.lua

@@ -220,7 +220,7 @@ local function bobOffset(phase)
 end
 
 local function tryImage(path)
-  local ok, img = pcall(love.graphics.newImage, require("src.render.Assets").resolve(path))
+  local ok, img = pcall(love.graphics.newImage, path)
   return ok and img or nil
 end