feat(opencode-web-terminal): complete OpenCode web terminal implementation

- Update OpenCode compose template with web server on port 3000
- Add default_port=3000 and interfaces=[terminal, web] to OpenCode seed data
- Remove hardcoded 8080 fallback in tunnel creation
- Fail gracefully when tool type has no default_port configured
- Update frontend ToolType API to include default_port, category, interfaces
- Add port, category, and interfaces fields to tool type creation form
- Display port and interfaces in tool type cards
- Create migration 0012 to make default_port non-nullable
- Set default_port values for existing built-in tool types
- Quality gates: typecheck ✓, build ✓, Python syntax ✓

openspec/changes/opencode-web-terminal/specs/opencode-web-server/spec.md

@@ -0,0 +1,39 @@
+## ADDED Requirements
+
+### Requirement: OpenCode runs a web server
+
+The system SHALL configure OpenCode containers to run a web server accessible on port 3000.
+
+#### Scenario: OpenCode container starts
+- **GIVEN** an OpenCode tool instance
+- **WHEN** the container starts
+- **THEN** a web server is running on port 3000 inside the container
+- **AND** the server serves a web terminal interface
+
+### Requirement: OpenCode exposes web interface
+
+The system SHALL mark OpenCode as having both terminal and web interfaces.
+
+#### Scenario: OpenCode instance created
+- **GIVEN** a new OpenCode instance
+- **WHEN** the instance list is displayed
+- **THEN** both "Open" and "Terminal" buttons are shown
+
+### Requirement: OpenCode web terminal uses correct port
+
+The system SHALL use port 3000 when creating tunnels for OpenCode instances.
+
+#### Scenario: Tunnel created for OpenCode
+- **GIVEN** an OpenCode instance with `default_port: 3000`
+- **WHEN** the instance starts and creates a tunnel
+- **THEN** the tunnel targets `http://container-name:3000`
+
+### Requirement: OpenCode web terminal displays properly
+
+The system SHALL serve a functional web terminal interface for OpenCode.
+
+#### Scenario: User opens OpenCode web UI
+- **GIVEN** a running OpenCode instance
+- **WHEN** the user clicks the "Open" button
+- **THEN** a new tab opens with the OpenCode web interface
+- **AND** the interface shows a terminal connected to the OpenCode process