Database schema & migration

[thaninbew]

Summary:

Create the Donation TypeORM entity and a reversible migration that creates the donations table. Wire the entity into the data source configuration.

Files to create:

• apps/backend/src/donations/donation.entity.ts (new)
• apps/backend/src/migrations/<timestamp>-add_donations.ts (new)
• apps/backend/src/data-source.ts (update to include entity and migration pattern, also update migration path ending to *.ts instead of *.js)

Acceptance criteria:

• Donation entity fields: id (PK serial), firstName, lastName, email, amount (numeric(10,2)), isAnonymous (boolean default false), donationType (enum: one_time | recurring), recurringInterval (nullable string "monthly" "yearly" "weekly" "bimonthly" "biweekly" ), dedicationMessage (nullable text), createdAt, updatedAt.
• Migration creates donations table in up() and drops it in down().
• data-source.ts includes Donation in entities and sets migrations pattern to apps/backend/src/migrations/*.ts.
• Running yarn docker:migrate:dev applies the migration; yarn docker:migrate:revert rolls it back.

Testing steps:

1. Start dev stack: yarn docker:up:dev
2. Run migration: yarn docker:migrate:dev
3. Check DB
4. Revert migration: yarn docker:migrate:revert