Ask to propagate OT info to all Pokémon when trainer identity changes

[Copilot]

Changing trainer Name/TID/SID on the Home page silently updated only the save file header — every existing Pokémon retained its old Original Trainer data. This adds a confirmation modal so the user can choose whether to bulk-apply the new identity to all Pokémon.

PKHeX.Facade — Trainer.cs

• PokemonInPartyCount / PokemonInBoxCount — non-empty slot counts used in the modal message
• ApplyOwnerToAll() — sets Owner.Name/TID/SID on every non-empty party + box Pokémon to the current trainer values, then calls Commit()

PKHeX.Web — Home.razor

• HandleNameChanged / HandleTIDChanged / HandleSIDChanged now defer the write: they store the mutation in _pendingTrainerChange and open the modal instead of applying immediately
• "Yes, update all" — invokes the pending change then calls ApplyOwnerToAll()
• "No, just update trainer" — invokes the pending change only; Pokémon OT data untouched

You have 6 Pokémon in your party and 42 in your box.
Would you like to update their Original Trainer info to match the new trainer values?

[ Yes, update all ]   [ No, just update trainer ]

PKHeX.Facade.Tests — TrainerTests.cs

• ApplyOwnerToAll_ShouldUpdateAllPokemon — sets trainer identity, calls ApplyOwnerToAll, save/reloads, and asserts every non-empty Pokémon carries the new Name, TID, and SID (p.Id.TID/SID rather than p.Owner.TID/SID because Owner.TID getter uses TrainerTID7, which is a Gen 7-style derived value and not symmetric with the DisplayTID setter for Gen 4 saves)