flaskpaste: initial commit with security hardening

Features:
- REST API for text/binary pastes with MIME detection
- Client certificate auth via X-SSL-Client-SHA1 header
- SQLite with WAL mode for concurrent access
- Automatic paste expiry with LRU cleanup

Security:
- HSTS, CSP, X-Frame-Options, X-Content-Type-Options
- Cache-Control: no-store for sensitive responses
- X-Request-ID tracing for log correlation
- X-Proxy-Secret validation for defense-in-depth
- Parameterized queries, input validation
- Size limits (3 MiB anon, 50 MiB auth)

Includes /health endpoint, container support, and 70 tests.

.gitignore

@@ -0,0 +1,48 @@
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+venv/
+ENV/
+.venv/
+
+# Testing
+.pytest_cache/
+.coverage
+htmlcov/
+.tox/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+
+# Data
+data/*.db
+data/*.db-journal
+data/*.db-wal
+data/*.db-shm
+
+# Secrets
+.credentials
+.credentials.json
+*.pem
+*.key
+
+# Build
+dist/
+build/
+*.egg-info/
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Private
+.claude/
+CLAUDE.md
+CRUSH.md
+PERSONAE