feat: implement docker infrastructure (US-001)

- Add docker-compose.yml with postgres, redis, api, and web services
- Add multi-stage Dockerfile for API (Python 3.11)
- Add multi-stage Dockerfile for web (Node.js 20 + nginx)
- Add Makefile with common development commands
- Add .env.example with all required environment variables
- Add placeholder pyproject.toml and package.json for builds
- Configure health checks for all services
- Setup persistent volumes for postgres, redis, and repos
- Run services as non-root users

openspec/specs/user-config/spec.md

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+# User Configuration Specification
+
+## Purpose
+
+Store and manage user preferences and settings.
+
+## Requirements
+
+### Requirement: Key-Value Storage
+
+The system SHALL store user configuration as JSONB key-value pairs.
+
+#### Scenario: Store preferences
+- GIVEN an authenticated user
+- WHEN they update their settings
+- THEN the configuration is stored in the UserConfig model
+
+### Requirement: Supported Config Keys
+
+The system SHALL support specific configuration keys.
+
+#### Scenario: Supported keys
+- GIVEN the configuration system
+- THEN these keys SHALL be supported:
+  - `default_editor`: Preferred code editor
+  - `theme`: UI theme preference
+  - `git_user_name`: Git commit author name
+  - `git_user_email`: Git commit author email
+
+### Requirement: Config Retrieval
+
+The system SHALL return user configuration.
+
+#### Scenario: Get config
+- GIVEN an authenticated user
+- WHEN they access settings
+- THEN their current configuration is returned
+
+### Requirement: Config Updates
+
+The system SHALL support partial configuration updates.
+
+#### Scenario: Update single key
+- GIVEN an authenticated user with existing config
+- WHEN they update just the theme
+- THEN only that key is modified
+- AND other keys remain unchanged
+
+### Requirement: Frontend Integration
+
+The system SHALL apply configuration in the frontend.
+
+#### Scenario: Apply theme
+- GIVEN a user with theme preference set
+- WHEN they load the application
+- THEN the selected theme is applied
+
+## Dependencies
+
+- Database models: UserConfig, User
+- auth-oauth (authenticated users)
+
+## Quality Gates
+
+- `pytest` must pass
+- `mypy .` must pass
+- `ruff check .` must pass
+- `npm run typecheck` must pass
+- `npm run lint` must pass