feat: ConnectWise PSA integration (#106)

PSA abstraction layer with provider pattern, ConnectWise integration (connection management, ticket linking, note posting, status updates, member mapping), Integrations page UI, Fernet credential encryption, in-memory TTL cache, 6 DB migrations, ConnectWise API reference docs.

backend/alembic/versions/058_add_psa_connections.py

@@ -0,0 +1,39 @@
+"""Add psa_connections table.
+
+Revision ID: 058
+Revises: 057
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision = "058"
+down_revision = "057"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "psa_connections",
+        sa.Column("id", postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column("account_id", postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column("provider", sa.String(50), nullable=False),
+        sa.Column("display_name", sa.String(100), nullable=False),
+        sa.Column("site_url", sa.String(255), nullable=False),
+        sa.Column("company_id", sa.String(100), nullable=False),
+        sa.Column("credentials_encrypted", sa.Text(), nullable=False),
+        sa.Column("is_active", sa.Boolean(), nullable=False, server_default=sa.text("true")),
+        sa.Column("last_validated_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.PrimaryKeyConstraint("id"),
+        sa.ForeignKeyConstraint(["account_id"], ["accounts.id"], ondelete="CASCADE"),
+        sa.UniqueConstraint("account_id"),
+    )
+    op.create_index("ix_psa_connections_account_id", "psa_connections", ["account_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_psa_connections_account_id")
+    op.drop_table("psa_connections")