Stream D: Security hardening — 10 fixes from QA review

- SEC-05: Fail fast if SECRET_KEY is default 'change-me-in-production'
- SEC-06: CORS allow_credentials=False (Bearer tokens don't need it)
- SEC-08: Input validation on auth schemas (min/max length, username pattern)
- SEC-10: .dockerignore files (root, backend, mcp-connector)
- SEC-11: Hardcode ALGORITHM='HS256' as constant, remove from settings
- CQ-01: Gate crawl scheduler on CRAWL_ENABLED env var (default false)
- OS-02: CONTRIBUTING.md
- OS-03: CHANGELOG.md with v1.0.0 entry
- setup.ps1: Add API_TOKEN generation (Windows parity with setup.sh)

backend/app/config.py

@@ -10,7 +10,7 @@ class Settings(BaseSettings):
 
     # Auth
     secret_key: str = "change-me-in-production"
-    algorithm: str = "HS256"
+    crawl_enabled: bool = False  # Set CRAWL_ENABLED=true to start program crawl scheduler
     access_token_expire_minutes: int = 1440  # 24 hours
     api_token: str = ""  # MCP connector auth — generated by setup.sh