v0.3.0-phase2 — network audit harness

Phase 2: the verification harness that makes the privacy guarantee testable.

• audit/checker.py: pure-stdlib, default-deny detection engine — a captured request is allowed only if an allowlist rule matches both the active scenario and the destination (subdomain-strict host globs, segment-aware path prefixes, mandatory reason per rule).
• audit/capture.py + scenarios/driver.py + audit.py: launch a Chromium binary behind mitmproxy (fresh profile, --disable-quic) and drive idle/navigation/bookmarks/history/downloads/settings/search.
• 24-case browserless self-test: a clean run passes; a leaky run (update ping, variations, safebrowsing, crash upload, lookalike host) is fully flagged. Wired into CI. Documents its honest limits (QUIC/raw UDP, OS DNS).