feat(tool-config): add categories, interfaces, and config management

Add support for tool categories, interface types, and per-tool configuration.

Backend:
- Add category and interfaces fields to ToolType model
- Create ToolConfig model for storing tool-specific settings
- Add tool_configs API endpoints (CRUD)
- Update built-in tool types with categories and interfaces:
  - code-server: editor, [web]
  - jupyter-notebook: notebook, [web]
  - opencode: ai-assistant, [terminal]
- Update instance API to include tool type interfaces
- Create Alembic migrations 0008 and 0009

Frontend:
- Update ToolType and Session interfaces with new fields
- Conditionally show Open/Terminal buttons based on tool interfaces
- Add API client for tool configs

OpenSpec: tool-config-management change created and implemented.

openspec/changes/tool-config-management/specs/tool-config-management/spec.md

@@ -0,0 +1,46 @@
+## ADDED Requirements
+
+### Requirement: Tool configs can be stored per user
+The system SHALL allow users to store configuration values for tool types.
+
+#### Scenario: Save global config
+- **WHEN** a user saves a config value for a tool type
+- **THEN** the config is stored with user_id and tool_type_id
+- **AND** it is available for all future instances of that tool
+
+#### Scenario: Save project-specific config
+- **WHEN** a user saves a config value with a project_id
+- **THEN** the config is scoped to that project
+- **AND** it overrides global config for that project
+
+### Requirement: Configs support env and file types
+The system SHALL support environment variable configs and file-based configs.
+
+#### Scenario: Env config
+- **WHEN** a config has type "env"
+- **THEN** it is injected as an environment variable when starting the container
+
+#### Scenario: File config
+- **WHEN** a config has type "file"
+- **THEN** it is written to a file in the container
+- **AND** the file path is configurable
+
+### Requirement: Tool types have categories and interfaces
+The system SHALL categorize tool types and declare their interfaces.
+
+#### Scenario: Web interface tool
+- **WHEN** a tool type has interface "web"
+- **THEN** the UI shows an "Open" button
+
+#### Scenario: Terminal interface tool
+- **WHEN** a tool type has interface "terminal"
+- **THEN** the UI shows a "Terminal" button
+
+### Requirement: OpenCode is available as built-in tool
+The system SHALL include OpenCode as a built-in tool type with terminal interface.
+
+#### Scenario: Create OpenCode instance
+- **WHEN** a user creates an OpenCode instance
+- **THEN** it starts a container with opencode installed
+- **AND** the repo is mounted at /workspace
+- **AND** the user can access it via terminal