feat(backend): default verify_tls to false for lab/redteam Mythic

flip default to False at model, API fallback, adapter, and factory layers.
add migration 0008 flipping c2_config.verify_tls server_default to false.
suppress urllib3 InsecureRequestWarning when verify_tls is off.
adapt c2 tests to new verify_tls default.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/migrations/versions/0008_c2_verify_tls_default_false.py

@@ -0,0 +1,33 @@
+"""flip c2_config.verify_tls server_default to false
+
+Revision ID: 0008_c2_verify_tls_default_false
+Revises: 0007
+Create Date: 2026-06-21 00:00:00.000000
+"""
+import sqlalchemy as sa
+from alembic import op
+
+revision = "0008_c2_verify_tls_default_false"
+down_revision = "0007"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    with op.batch_alter_table("c2_config") as batch_op:
+        batch_op.alter_column(
+            "verify_tls",
+            existing_type=sa.Boolean(),
+            existing_nullable=False,
+            server_default=sa.false(),
+        )
+
+
+def downgrade() -> None:
+    with op.batch_alter_table("c2_config") as batch_op:
+        batch_op.alter_column(
+            "verify_tls",
+            existing_type=sa.Boolean(),
+            existing_nullable=False,
+            server_default=sa.true(),
+        )