[Enhancement] Add DB migrations for SQLite

[moisesPompilio]

Describe the enhancement
After PR #804 introduced SQLite into Floresta, the schema is currently created via static DDL. Replace that with a versioned migrations system so schema changes are applied incrementally and safely instead of requiring destructive changes / hardforks.

Use case

• Evolve tables (add/remove columns) without breaking existing installations.
• Automatically apply only pending migrations on startup or via a controlled migration step.
• Make schema changes auditable and reversible.

Additional context
Recommend using refinery for migrations: https://docs.rs/refinery/latest/refinery/

• Add a migrations/ folder with versioned SQL (e.g. V1__initial.sql, V2__add_column_xyz.sql).
• Ensure an initial migration reproduces the schema introduced in PR Wallet: move database to sqlite, remove kv and memmory db #804.

[luisschwab]

@moisesPompilio do we still need this after your BDK PR? My understanding is that the only extra data we need apart from BDK's own persistence is Electrum-specific data.

Can you close this one if the above is correct?

[moisesPompilio]

Yeah; closing this issue because we'll have an architectural change in the watch-only feature. Therefore, if any persistence using SQLite is implemented, it should already include migrations.