feat(weather)!: add /thuyvan flood alerts for Tân Thuận

/thuyvan shows the 5-day tide-peak forecast at Phú An and Nhà Bè from
the Đài KTTV Nam Bộ bulletin PDF, the Open-Meteo rain forecast, and live
VNDMS river gauges within 30 km. /thuyvan_subscribe opts a chat into a
10:30 ICT push, retried at 12:30, sent only when a forecast peak reaches
báo động I (1.40 m) or a day's rain reaches 50 mm. A missing or stale
bulletin fails the push instead of reading as no risk.

The thoitiet module is renamed to weather; the /thoitiet* commands keep
their names.

BREAKING CHANGE: the module key is now "weather". A MODULES list that
names thoitiet fails at startup and must name weather instead.

.env.example

@@ -15,7 +15,7 @@ MONGO_DATABASE=miti99bot
 # Comma-separated module list. Empty = load every module, including any module
 # added later — so list them explicitly when a deployment should only gain a new
 # module deliberately.
-MODULES=util,misc,random,amlich,wordle,loldle,lol,stock,gold,coin,stats,monkeyd,sticker,alias,blacklist
+MODULES=util,misc,random,amlich,wordle,loldle,lol,stock,gold,coin,stats,monkeyd,sticker,alias,blacklist,weather
 # Telegram user id for owner-only commands (renamed from BOT_OWNER_ID).
 OWNER_ID=
 # Comma-separated admin Telegram user ids (renamed from ADMIN_USER_IDS).