fix(auth): change users.id and user_id FKs from uuid to text

Better-Auth generates nanoid-style text IDs (e.g. pGud2ln2WAFHC0KYjBVKR4Rc7mM8OcTI),
but the users table was using PostgreSQL uuid type, causing INSERT failures on
registration. This changes User.id, UserStoreAccount.user_id, and Purchase.user_id
from uuid to text, with a corresponding Alembic migration.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

api/alembic/versions/003_fix_user_id_text.py

@@ -0,0 +1,53 @@
+"""Change users.id and FK columns from uuid to text.
+
+Better-Auth generates nanoid-style text IDs (e.g. pGud2ln2WAFHC0KYjBVKR4Rc7mM8OcTI),
+but the users table was using PostgreSQL uuid type, causing INSERT failures.
+
+Revision ID: 003_fix_user_id_text
+Revises: 002_better_auth_tables
+Create Date: 2026-03-31
+"""
+
+import sqlalchemy as sa
+from sqlalchemy import text
+
+from alembic import op
+
+revision = "003_fix_user_id_text"
+down_revision = "002_better_auth_tables"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Step 1: Drop FK constraints that reference users.id
+    op.execute(text("ALTER TABLE user_store_accounts DROP CONSTRAINT IF EXISTS user_store_accounts_user_id_fkey"))
+    op.execute(text("ALTER TABLE purchases DROP CONSTRAINT IF EXISTS purchases_user_id_fkey"))
+
+    # Step 2: Alter users.id from uuid to text
+    op.alter_column("users", "id", existing_type=sa.UUID(), type_=sa.Text(), existing_nullable=False, postgresql_using="id::text")
+
+    # Step 3: Alter user_store_accounts.user_id from uuid to text
+    op.alter_column("user_store_accounts", "user_id", existing_type=sa.UUID(), type_=sa.Text(), existing_nullable=False, postgresql_using="user_id::text")
+
+    # Step 4: Alter purchases.user_id from uuid to text
+    op.alter_column("purchases", "user_id", existing_type=sa.UUID(), type_=sa.Text(), existing_nullable=False, postgresql_using="user_id::text")
+
+    # Step 5: Re-add FK constraints
+    op.execute(text("ALTER TABLE user_store_accounts ADD CONSTRAINT user_store_accounts_user_id_fkey FOREIGN KEY (user_id) REFERENCES users(id)"))
+    op.execute(text("ALTER TABLE purchases ADD CONSTRAINT purchases_user_id_fkey FOREIGN KEY (user_id) REFERENCES users(id)"))
+
+
+def downgrade() -> None:
+    # Drop FK constraints
+    op.execute(text("ALTER TABLE purchases DROP CONSTRAINT IF EXISTS purchases_user_id_fkey"))
+    op.execute(text("ALTER TABLE user_store_accounts DROP CONSTRAINT IF EXISTS user_store_accounts_user_id_fkey"))
+
+    # Alter back to UUID
+    op.alter_column("purchases", "user_id", existing_type=sa.Text(), type_=sa.UUID(), existing_nullable=False, postgresql_using="user_id::uuid")
+    op.alter_column("user_store_accounts", "user_id", existing_type=sa.Text(), type_=sa.UUID(), existing_nullable=False, postgresql_using="user_id::uuid")
+    op.alter_column("users", "id", existing_type=sa.Text(), type_=sa.UUID(), existing_nullable=False, postgresql_using="id::uuid")
+
+    # Re-add FK constraints
+    op.execute(text("ALTER TABLE user_store_accounts ADD CONSTRAINT user_store_accounts_user_id_fkey FOREIGN KEY (user_id) REFERENCES users(id)"))
+    op.execute(text("ALTER TABLE purchases ADD CONSTRAINT purchases_user_id_fkey FOREIGN KEY (user_id) REFERENCES users(id)"))