security: Fix 10 vulnerabilities, remove 12 dead code instances

Critical fixes:
- Remove hardcoded admin/admin123 credentials from UserManager
- Enable JWT signature verification (was disabled for debugging)
- Redact secrets from /dev/config endpoint (was exposing os.environ)
- Remove hardcoded SSH admin/admin credentials from hardware service
- Add channel validation to prevent command injection in router interface

Rust fixes:
- Replace partial_cmp().unwrap() with .unwrap_or(Equal) to prevent
  NaN panics in 6 locations across core, signal, nn, mat crates
- Replace .expect()/.unwrap() with safe fallbacks in utils, csi_receiver
- Replace SystemTime unwrap with unwrap_or_default

Dead code removed:
- Duplicate imports (CORSMiddleware, os, Path, ABC, subprocess)
- Unused AdaptiveRateLimit/RateLimitStorage/RedisRateLimitStorage (~110 lines)
- Unused _log_authentication_event method
- Unused Confidence::new_unchecked in Rust
- Fix bare except: clause to except Exception:

https://claude.ai/code/session_01Ki7pvEZtJDvqJkmyn6B714

v1/src/api/routers/stream.py

@@ -17,16 +17,13 @@ from src.api.dependencies import (
     get_current_user_ws,
     require_auth
 )
-from src.api.websocket.connection_manager import ConnectionManager
+from src.api.websocket.connection_manager import connection_manager
 from src.services.stream_service import StreamService
 from src.services.pose_service import PoseService
 
 logger = logging.getLogger(__name__)
 router = APIRouter()
 
-# Initialize connection manager
-connection_manager = ConnectionManager()
-
 
 # Request/Response models
 class StreamSubscriptionRequest(BaseModel):