feat: add Seed Vault support (multi-container: Bank + Seed Vault)

[matt-finney]

What

• Adds Seed Vault as an additional source alongside the Bank.
• Listens to ItemContainerID.SEED_VAULT.
• Snapshots, Compare, Search, Export all work per source.

Behavior

• No changes to existing Bank behavior.
• UI adds a simple dropdown (Bank | Seed Vault).
• Seed Vault requires opening the Seed Vault UI (same as Bank needing the bank open).

Storage/Migration

• Snapshots are stored separately per source to avoid mixing.
• Existing bank snapshots are preserved (non-breaking).

Notes

• Pricing (GE/HA) unchanged.
• Bank-only filler filters are skipped for Seed Vault.