chore(security): drop passlib for direct bcrypt + reject CLI-flag check targets

- Replace passlib.CryptContext with bcrypt 4.2.1 directly (passlib is
  unmaintained and only emitted warnings when paired with bcrypt 4+).
  hash_password / verify_password now call bcrypt.checkpw / .hashpw, and
  verify_password is hardened against empty inputs without raising.
  scripts/hash_password.py + tests/conftest.py updated to match.
- status_checker.check_node() now rejects targets starting with '-' before
  any subprocess invocation, defending ping/tcp paths against arg-injection
  if an admin sets a check_target like '-O'.

Tests added:
- test_auth: expired JWT, malformed JWT, wrong-secret JWT, empty password
  vs empty server hash, verify_password edge cases.
- test_scan: _background_scan failure path marks ScanRun failed, leaves
  non-running terminal status alone, success path invokes run_scan.
- test_status_checker: ping/tcp invocations are bypassed when target or
  ip starts with '-'.

Backend coverage 89% → 90%.

backend/app/core/security.py

@@ -1,22 +1,22 @@
 from datetime import datetime, timedelta, timezone
 
+import bcrypt
 from jose import JWTError, jwt
-from passlib.context import CryptContext
 
 from app.core.config import settings
 
-pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
-
 
 def verify_password(plain: str, hashed: str) -> bool:
+    if not plain or not hashed:
+        return False
     try:
-        return bool(pwd_context.verify(plain, hashed))
-    except ValueError:
+        return bcrypt.checkpw(plain.encode("utf-8"), hashed.encode("utf-8"))
+    except (ValueError, TypeError):
         return False
 
 
 def hash_password(password: str) -> str:
-    return str(pwd_context.hash(password))
+    return bcrypt.hashpw(password.encode("utf-8"), bcrypt.gensalt()).decode("utf-8")
 
 
 def create_access_token(subject: str) -> str: