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/web/src/api/tool_types.ts

@@ -7,6 +7,7 @@ export interface ToolType {
   description: string | null;
   category: string;
   interfaces: string[];
+  default_port: number | null;
   compose_template: string;
   required_variables: string[];
   is_builtin: boolean;