Add targeted coverage for the stat-rise message translation fix

No existing test could tell a translated stat name apart from a raw
stat:upper() that never went through Strings() at all: every rose!
message assertion in the suite runs with no catalog loaded, where
Strings() is an identity function either way.

Loads a real catalog (Strings.load) that translates one stat name at a
time and checks it actually reaches the X-item, vitamin, and AI-trainer
X-item messages -- ROM-free, over tests/fixture_data. Confirmed this
catches the regression: reverting src/inventory/ItemEffects.lua and
src/battle/TrainerAI.lua to their pre-fix state fails 5 of 6 checks.

tests/engine/stat_rise_message_translation_test.lua

@@ -0,0 +1,73 @@
+-- The stat name substituted into X-item/vitamin "rose!" messages must
+-- itself reach a translation catalog, not just the surrounding sentence
+-- template (src/inventory/ItemEffects.lua, src/battle/TrainerAI.lua).
+-- With no catalog loaded it stays English (the existing baseline); with
+-- one loaded that translates e.g. "ATTACK", the substituted word must
+-- change too -- that is the actual bug this suite guards against, which
+-- passing/failing sentences alone (as other suites already check)
+-- cannot tell apart from a raw stat:upper() that was never wrapped in
+-- Strings() at all.
+package.path = "./?.lua;./?/init.lua;" .. package.path
+
+local T = require("tests.modkit")
+local Data = T.fixtures.fresh()
+local Pokemon = require("src.pokemon.Pokemon")
+local SaveData = require("src.core.SaveData")
+local ItemEffects = require("src.inventory.ItemEffects")
+local TrainerAI = require("src.battle.TrainerAI")
+local Strings = require("src.core.Strings")
+
+local function withCatalog(catalog, fn)
+  Strings.load({ strings = catalog })
+  local ok, err = pcall(fn)
+  Strings.load(nil)
+  if not ok then error(err, 0) end
+end
+
+-- ------------------------------------------------------- player X-item
+
+local save = SaveData.newGame()
+local player = { name = "FIXMON", stages = {} }
+local xBattle = { player = player, kind = "wild" }
+
+local _, baseline = ItemEffects.use(Data, save, "X_ATTACK", nil, xBattle)
+T.check(baseline[1]:find("ATTACK", 1, true) ~= nil,
+  "X ATTACK's rose! message names the stat in English with no catalog")
+
+withCatalog({ ATTACK = "ATTAQUE" }, function()
+  player.stages.attack = nil
+  local _, msgs = ItemEffects.use(Data, save, "X_ATTACK", nil, xBattle)
+  T.check(msgs[1]:find("ATTAQUE", 1, true) ~= nil,
+    "a catalog translating ATTACK reaches the X ATTACK rose! message")
+  T.check(msgs[1]:find("ATTACK", 1, true) == nil,
+    "...and the untranslated English stat name is gone")
+end)
+
+-- --------------------------------------------------------- player vitamin
+
+local target = Pokemon.new(Data, "FIXMON_A", 10)
+withCatalog({ DEFENSE = "DEFENSE_FR" }, function()
+  local _, msgs = ItemEffects.use(Data, save, "IRON", target)
+  T.check(msgs[1]:find("DEFENSE_FR", 1, true) ~= nil,
+    "a catalog translating DEFENSE reaches the IRON (vitamin) rose! message")
+end)
+
+local hpTarget = Pokemon.new(Data, "FIXMON_A", 10)
+withCatalog({ HP = "PV" }, function()
+  local _, msgs = ItemEffects.use(Data, save, "HP_UP", hpTarget)
+  T.check(msgs[1]:find("PV", 1, true) ~= nil,
+    "a catalog translating HP reaches the HP UP rose! message")
+end)
+
+-- ------------------------------------------------------- AI trainer X-item
+
+local enemy = { name = "FOE", stages = {} }
+local aiBattle = { enemy = enemy, trainer = { name = "TRAINER" }, data = Data }
+
+withCatalog({ SPEED = "VITESSE" }, function()
+  local msgs = TrainerAI.useItem(aiBattle, "X_SPEED")
+  T.check(msgs[2]:find("VITESSE", 1, true) ~= nil,
+    "a catalog translating SPEED reaches the AI trainer's X SPEED rose! message")
+end)
+
+T.finish("stat rise message translation")