feat: add pokemon_form_flavor_text (per-form flavor text)

[MiquelRForgeFlow]

Summary

Adds a new PokemonFormFlavorText model/table, exposing flavor_text_entries on /pokemon-form/{id}. It mirrors the existing species-level pokemon_species_flavor_text, so forms that had their own Pokédex entries can carry them explicitly.

Scope

Populated for Generation III only, the earliest generation with form-specific Pokédex entries:

• Gen I–II: no form-specific entries.
• Gen III: Deoxys is the only case. Its forme was fixed per game version, so each version's entry is really a forme's entry:
  • Ruby / Sapphire → Normal Forme
  • FireRed → Attack Forme
  • LeafGreen → Defense Forme
  • Emerald → Speed Forme

Later generations have more form-specific entries and are intentionally left for follow-up PRs, which keeps this one small and easy to review.

Text is copied verbatim (including line breaks and page-break characters) from the matching pokemon_species_flavor_text rows, re-keyed to the correct pokemon_form_id. English is the only language present for these entries.

Changes

• New PokemonFormFlavorText model + migration.
• Serializer: flavor_text_entries on the pokemon-form detail endpoint.
• build.py loader + pokemon_form_flavor_text.csv (5 rows).
• OpenAPI / Hasura metadata updated.

Open question for reviewers

These 5 Gen III Deoxys entries currently also live in pokemon_species_flavor_text (versions 7–11), where they read as generic species entries even though they're really forme-specific.

I've kept them in place, because:

• They match what each Gen III game actually shows (the forme was version-locked, so the per-version species entry is accurate for that game).
• /pokemon-species/deoxys is the common path consumers read; removing them would leave the species with no Gen III flavor text, which is a backwards-incompatible change.

That said, one could argue they're now redundant and better represented here, so they could be dropped from the species table. I'm happy to do that (here or in a follow-up) if maintainers prefer. I'm flagging it so you can decide.

AI coding assistance disclosure

Checking everything I did is fine.

Contributor check list

• I have written a description of the contribution and explained its motivation.
• I have written tests for my code changes (if applicable).
• I have read and understood the AI Assisted Contribution guidelines.
• I will own this change in production, and I am prepared to fix any bugs caused by my code change.