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/config/settings.py

@@ -77,6 +77,8 @@ class Settings(BaseSettings):
     wifi_interface: str = Field(default="wlan0", description="WiFi interface name")
     csi_buffer_size: int = Field(default=1000, description="CSI data buffer size")
     hardware_polling_interval: float = Field(default=0.1, description="Hardware polling interval in seconds")
+    router_ssh_username: str = Field(default="admin", description="Default SSH username for router connections")
+    router_ssh_password: str = Field(default="", description="Default SSH password for router connections (set via ROUTER_SSH_PASSWORD env var)")
     
     # CSI Processing settings
     csi_sampling_rate: int = Field(default=1000, description="CSI sampling rate")