feat(tenant): add tenant_domains allowlist and /v1/domains management API

Why:
- Domain values are denormalized into every Qdrant point payload. Without
  validation, an unregistered or typo'd domain (e.g. "fier" for "fire")
  silently creates a new partition that retrieval never queries — the file
  ends up invisible rather than rejected. Tenants also need independently
  sized domain sets (one may run 14 insurance lines, another 6), which rules
  out an enum.

Changes:
- tenant_domains table (migration 41335d162de8) + repository, unique on
  (tenant_id, domain).
- src/application/domains/: ensure_domain_allowed() is the strict-allowlist
  check now run inside upload_source_file()'s first transaction, before any
  MinIO object, job row, or Qdrant point is written.
- /v1/domains (list/create/patch/disable/enable) gated on its own
  domains:read/domains:write scopes, deliberately separate from files:write
  so an upload key cannot create partitions. domain itself is immutable
  (denormalized into every point payload); only display_name is editable.
  Disable blocks new uploads without touching already-indexed points.

Impact:
- BREAKING: POST /v1/files now rejects any domain without an active
  tenant_domains row (400, unknown_domain). A domain must be created via
  POST /v1/domains before the first upload to it.

alembic/versions/41335d162de8_create_tenant_domains.py

@@ -0,0 +1,48 @@
+"""create tenant_domains
+
+Revision ID: 41335d162de8
+Revises: bfc6c81c2542
+Create Date: 2026-08-20 17:48:29.443293
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = '41335d162de8'
+down_revision: Union[str, Sequence[str], None] = 'bfc6c81c2542'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('tenant_domains',
+    sa.Column('id', sa.Uuid(), nullable=False),
+    sa.Column('tenant_id', sa.Uuid(), nullable=False),
+    sa.Column('domain', sa.String(length=80), nullable=False),
+    sa.Column('display_name', sa.String(length=200), nullable=False),
+    sa.Column('status', sa.String(length=20), server_default='active', nullable=False),
+    sa.Column('metadata', postgresql.JSONB(astext_type=sa.Text()), server_default='{}', nullable=False),
+    sa.Column('created_at', sa.DateTime(timezone=True), server_default=sa.text('now()'), nullable=False),
+    sa.Column('updated_at', sa.DateTime(timezone=True), server_default=sa.text('now()'), nullable=False),
+    sa.Column('disabled_at', sa.DateTime(timezone=True), nullable=True),
+    sa.CheckConstraint("status IN ('active', 'disabled')", name='ck_tenant_domains_status'),
+    sa.ForeignKeyConstraint(['tenant_id'], ['tenants.id'], ondelete='CASCADE'),
+    sa.PrimaryKeyConstraint('id'),
+    sa.UniqueConstraint('tenant_id', 'domain', name='uq_tenant_domains_tenant_id_domain')
+    )
+    op.create_index(op.f('ix_tenant_domains_tenant_id'), 'tenant_domains', ['tenant_id'], unique=False)
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f('ix_tenant_domains_tenant_id'), table_name='tenant_domains')
+    op.drop_table('tenant_domains')
+    # ### end Alembic commands ###