fix(proxy): use internal container port instead of host port

The proxy was using instance.port which is a dynamically allocated
host port (e.g., 10001). But containers communicate on the Docker
network using their internal ports (8443 for code-server, 8888 for
jupyter). This caused connection failures when opening instances.

- Add default_port field to ToolType model (null for terminal-only tools)
- Create migration 0010 for default_port column
- Update seed data: code-server=8443, jupyter=8888, opencode=null
- Update proxy to use tool type's default_port instead of instance.port
- Update frontend ToolType interface to include default_port

Fixes: Opening instances now routes to correct internal container port

apps/api/alembic/versions/0010_tool_type_default_port.py

@@ -0,0 +1,28 @@
+"""add default_port to tool_types
+
+Revision ID: 0010_tool_type_default_port
+Revises: 0009_tool_configs
+Create Date: 2026-05-20 10:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision: str = "0010_tool_type_default_port"
+down_revision: Union[str, None] = "0009_tool_configs"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "tool_types",
+        sa.Column("default_port", sa.Integer(), nullable=True)
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("tool_types", "default_port")