## Why

Tool instances need runtime configuration and secrets (API keys, database passwords, etc.). The backend has Config and Secret models (FN-004), but there's no UI for users to manage these values, and no runtime injection mechanism to pass them into spawned containers.

## What Changes

- **Config management UI**: Frontend pages for creating, updating, and deleting config values at global/user/project/instance scopes
- **Secret management UI**: Frontend pages for encrypted secret storage with masked value display
- **Runtime injection**: Backend service that mounts configs and secrets into tool containers at spawn time
- **Scope-based access control**: Configs/secrets respect scope hierarchy (global → user → project → instance)
- **Encryption verification**: Ensure Fernet encryption is properly applied to all secret values

## Capabilities

### New Capabilities
- `config-management`: CRUD operations for configuration values with scope support
- `secret-management`: Encrypted storage and retrieval of sensitive values
- `runtime-injection`: Mount configs and secrets into tool containers at spawn

### Modified Capabilities
- None (extends existing Config/Secret models)

## Impact

- **apps/web/src/**: New config and secret management pages
- **apps/api/app/routers/configs.py**: Enhanced with scope filtering
- **apps/api/app/routers/secrets.py**: Enhanced with scope filtering
- **apps/api/app/services/**: New runtime injection service
- **apps/api/app/models/**: Potential Config/Secret model updates for scope validation