Add confidence-rated local device identification

[Adam-Ghanem]

What changed

• identifies responding devices with a best-effort name, device type, operating-system hint, confidence, and supporting evidence
• uses bounded local reverse DNS, NetBIOS, ARP-neighbor, and observed TTL signals without an external API key
• persists identity fields through SQLite schema v8 and surfaces them in scans, host checks, inventory, and reports
• keeps the scan authorization boundary and labels uncertain inferences explicitly

Why

Network scan results previously returned only an IP, reachability state, and generic details. Operators could not quickly understand what kind of device had replied or how reliable an OS guess was.

Validation

• 175 tests passed on the exact pushed branch
• Flake8 passed
• Mypy passed
• Bandit passed
• frontend JavaScript syntax check passed
• git diff --check passed