feat(modules): port wordle module + per-subject locking

Phase 5b of go-port-cloud-run plan. Port 14855-word dictionary
(89 KB, byte-identical to JS source) and four wordle commands
(/wordle, /wordle_new, /wordle_giveup, /wordle_stats).

KV wire-format parity: GameState/Stats JSON match JS shape;
*int64 LastResultAt for null-value compatibility. Two real bugs
caught and fixed: (1) defaultRNG data race in handlers — switched
to math/rand.Intn (mutex-protected package-level); (2) Get→mutate→Put
logical race in groups — added per-subject sync.Mutex map to serialize
access. TTL deferred (Firestore has no expirationTtl equiv — Phase 11 GC).

internal/modules/wordle/wordle.go

@@ -0,0 +1,41 @@
+package wordle
+
+import (
+	"github.com/tiennm99/miti99bot-go/internal/modules"
+)
+
+// New is the wordle module Factory. Loads the embedded dictionary once,
+// captures the per-module KV via closure, and registers all four commands.
+func New(deps modules.Deps) modules.Module {
+	words, set := loadWords()
+	s := &state{kv: deps.KV, words: words, set: set}
+
+	return modules.Module{
+		Commands: []modules.Command{
+			{
+				Name:        "wordle",
+				Visibility:  modules.VisibilityPublic,
+				Description: "Classic wordle — guess the 5-letter word",
+				Handler:     s.handleWordle,
+			},
+			{
+				Name:        "wordle_new",
+				Visibility:  modules.VisibilityPublic,
+				Description: "Start a new round (auto-gives-up any in-progress one)",
+				Handler:     s.handleNew,
+			},
+			{
+				Name:        "wordle_giveup",
+				Visibility:  modules.VisibilityPublic,
+				Description: "Reveal the current wordle answer",
+				Handler:     s.handleGiveup,
+			},
+			{
+				Name:        "wordle_stats",
+				Visibility:  modules.VisibilityPublic,
+				Description: "Show your wordle stats (wins, streak)",
+				Handler:     s.handleStats,
+			},
+		},
+	}
+}