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/git-repo/spec.md

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+# Git Repository Management Specification
+
+## Purpose
+
+Manage git repositories as bare repos on disk with metadata in database.
+
+## Requirements
+
+### Requirement: Repository Creation
+
+The system SHALL allow creating new bare git repositories.
+
+#### Scenario: Create repository
+- GIVEN an authenticated user with a project
+- WHEN they create a new repository
+- THEN a bare repo is initialized on disk at `/data/repos/{user_id}/{project_id}/{repo_name}.git`
+- AND metadata is stored in the database
+
+### Requirement: Repository Cloning
+
+The system SHALL support cloning external repositories.
+
+#### Scenario: Clone repository
+- GIVEN an authenticated user with a project
+- WHEN they provide a remote URL
+- THEN the system clones as a bare mirror
+- AND stores it in the structured path
+
+### Requirement: Repository Listing
+
+The system SHALL list all user repositories.
+
+#### Scenario: List repositories
+- GIVEN an authenticated user
+- WHEN they view the repositories page
+- THEN all their repos are listed with name, path, and last push date
+
+### Requirement: Repository Deletion
+
+The system SHALL support repository deletion.
+
+#### Scenario: Delete repository
+- GIVEN an authenticated user
+- WHEN they delete a repository
+- THEN it's removed from disk
+- AND the database record is deleted
+
+### Requirement: Duplicate Prevention
+
+The system SHALL prevent duplicate repository names per project.
+
+#### Scenario: Duplicate name
+- GIVEN a project with a repo named "frontend"
+- WHEN the user tries to create another "frontend" repo
+- THEN the system rejects with a validation error
+
+## Dependencies
+
+- Database models: GitRepository, Project, User
+- Docker volume for repo storage
+
+## Quality Gates
+
+- `pytest` must pass
+- `mypy .` must pass
+- `ruff check .` must pass
+- `npm run typecheck` must pass
+- `npm run lint` must pass