fix: model Minior meteor/core forms consistently

[MiquelRForgeFlow]

(Follow-up of #1616)

Give all 14 Minior forms is_battle_only=0 and a Shields Down condition whose base_form points to the same-colour counterpart (meteor <-> core), so the shield/core toggle is represented in both directions.

All 14 Minior forms (7 Meteor + 7 Core) are marked is_battle_only = 0, since neither is strictly battle-only: outside of battle a wild Minior appears in its Meteor form while a caught one shows its Core, so both forms can be seen outside of battle. The Shields Down toggle between them is instead captured by the trigger_conditions, with each form's base_form pointing to its same-colour counterpart (Meteor ↔ Core).

Which form is shown outside of battle (wild → Meteor, caught → Core) isn't something the current form model can express; it would need an extra configuration (a wild-vs-caught default form). That's out of scope here, but the same mechanism would also cover Gimmighoul (Chest vs Roaming), so it may be worth considering as a separate, follow-up feature.

AI coding assistance disclosure

Checking numbers and generating PR description.

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.