feat: add config module with environment variable handling
Implements Step 1.1 config.py with Pydantic Settings:
- PORT (default 3366), DB_PATH, BASE_PATH
- AUTH_HEADER_NAME, TRUSTED_PROXY_IPS (comma-separated)
- CSRF_SECRET (required), CSRF_COOKIE_NAME
- SEED_ON_START, LOG_LEVEL (validated), METRICS_ENABLED
Includes 28 TDD tests covering defaults, overrides, and validation.
Also fixes pytest pythonpath configuration.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Petru Paler
61f704c68d