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/types.gen.go

@@ -3472,7 +3472,7 @@ type ReactionTypeEmoji struct {
 	// Type of the reaction, always “emoji”
 	Type ReactionTypeKind `json:"type"`
 	// Reaction emoji. Currently, it can be one of "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", ""
-	Emoji string `json:"emoji"`
+	Emoji ReactionEmoji `json:"emoji"`
 }
 
 // MarshalJSON encodes ReactionTypeEmoji with the discriminator field