feat: implement Fitbit OAuth, Garmin MFA, and optimize segment discovery

- Add Fitbit authentication flow (save credentials, OAuth callback handling)
- Implement Garmin MFA support with successful session/cookie handling
- Optimize segment discovery with new sampling and activity query services
- Refactor database session management in discovery API for better testability
- Enhance activity data parsing for charts and analysis
- Update tests to use testcontainers and proper dependency injection
- Clean up repository by ignoring and removing tracked transient files (.pyc, .db)

.gitignore

@@ -0,0 +1,58 @@
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+env/
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+
+# Virtual Environment
+.venv/
+venv/
+ENV/
+
+# Databases
+*.db
+*.sqlite3
+
+# Logs
+*.log
+test_log_*.txt
+coverage_report.txt
+pytest_output.txt
+
+# Security/Secrets
+*.env
+.env.*
+*.pem
+*.key
+id_rsa
+secrets/
+
+# IDEs
+.vscode/
+.idea/
+
+# Tooling
+.agent/
+.kilocode/
+.qwen/
+.pytest_cache/
+.mypy_cache/
+.coverage
+htmlcov/