refactor(api): typed enums for emoji-list fields (DiceEmoji, ReactionEmoji)

Two API fields carry restricted emoji-value sets that the scraper's
curly-quote regex strips during IR extraction (multi-byte boundary
issue): ReactionTypeEmoji.Emoji and sendDice.Emoji. They previously
typed as plain string with no compile-time guarantee on values.

Add hand-curated typed-string enums in api/enums.go (the manual file,
not enums.gen.go):

  - DiceEmoji: 6 constants (Dice, Dart, Basketball, Football, Bowling,
    SlotMachine) covering Telegram's full set for sendDice.
  - ReactionEmoji: 73 constants covering the canonical reaction set
    from https://core.telegram.org/bots/api#reactiontypeemoji. Names
    follow Unicode CLDR short names where one exists, otherwise stable
    common-English labels (e.g. ThumbsUp, Heart, Clown, ManTechnologist).

Wire the field-type override via cmd/genapi/emitter.go:

  - fieldTypeOverrides map keyed "<TypeOrParamsName>.<FieldName>".
  - goField/multipartFieldEntry consult the override after the enum-plan
    lookup; falls through to the default goType when nothing matches.
  - methods.tmpl gains goFieldP/multipartFieldEntryP helpers that pass
    the params type name as override-parent (the params struct doesn't
    share a Go type with the field, so the existing parent="" enum-key
    convention is preserved).

Regenerated api/types.gen.go and api/methods.gen.go now type the two
fields as ReactionEmoji and DiceEmoji respectively. No other Emoji
field is affected (override is scoped per parent type). regen-from-
fixture is byte-deterministic across runs.

Add api/emoji_enums_test.go covering const wire values, reflection
checks on field types, and a marshal/unmarshal round-trip for
ReactionTypeEmoji.

api/methods.gen.go

@@ -1953,7 +1953,7 @@ type SendDiceParams struct {
 	// Identifier of the direct messages topic to which the message will be sent; required if the message is sent to a direct messages chat
 	DirectMessagesTopicID *int64 `json:"direct_messages_topic_id,omitempty"`
 	// Emoji on which the dice throw animation is based. Currently, must be one of “”, “”, “”, “”, “”, or “”. Dice can have values 1-6 for “”, “” and “”, values 1-5 for “” and “”, and values 1-64 for “”. Defaults to “”
-	Emoji string `json:"emoji,omitempty"`
+	Emoji DiceEmoji `json:"emoji,omitempty"`
 	// Sends the message silently. Users will receive a notification with no sound.
 	DisableNotification *bool `json:"disable_notification,omitempty"`
 	// Protects the contents of the sent message from forwarding