Fix 12 security findings from adversarial audit

CRITICAL:
- #1+#2: Consistency proof verification no longer a stub — implements
  actual hash chain reconstruction from proof hashes, rejects proofs
  that don't reconstruct to the expected root. GossipNode._verify_consistency
  now calls verify_consistency_proof() instead of just checking sizes.
- #3: Remove passphrase.lower() from KDF — was silently discarding
  case entropy from mixed-case passphrases. Passphrases are now
  case-sensitive as users would expect.
- #4: Federation gossip now applies record_filter (trust store check)
  on every received record before appending to the log. Untrusted
  attestor fingerprints are rejected with a warning.
- #5: Killswitch disables all logging BEFORE activation to prevent
  audit log from recording killswitch activity that could survive an
  interrupted purge. Audit log destruction moved to position 4 (right
  after keys + flask secret, before other data).

HIGH:
- #6: CSRF exemption narrowed from entire dropbox blueprint to only
  the upload view function. Admin routes retain CSRF protection.
- #7: /health endpoint returns only {"status":"ok"} to anonymous
  callers. Full operational report requires authentication.
- #8: Metadata stripping now reconstructs image from pixel data only
  (Image.new + putdata), stripping XMP, IPTC, and ICC profiles — not
  just EXIF.
- #9: Same as #6 (CSRF scope fix).

MEDIUM:
- #11: Receipt HMAC key changed from public upload token to server-side
  secret key, making valid receipts unforgeable by the source or anyone
  who captured the upload URL.
- #12: Docker CMD no longer defaults to --no-https. HTTPS with
  self-signed cert is the default; --no-https requires explicit opt-in.
- #14: shred return code now checked — non-zero exit falls through to
  the zero-overwrite fallback instead of silently succeeding.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/docker/Dockerfile

@@ -73,8 +73,9 @@ EXPOSE 5000 8000
 
 USER soosef
 
-# Init on first run, then start web UI + federation API
-CMD ["sh", "-c", "soosef init 2>/dev/null; soosef serve --host 0.0.0.0 --no-https"]
+# Init on first run, then start web UI (HTTPS by default with self-signed cert).
+# Use --no-https explicitly if running behind a TLS-terminating reverse proxy.
+CMD ["sh", "-c", "soosef init 2>/dev/null; soosef serve --host 0.0.0.0"]
 
 HEALTHCHECK --interval=30s --timeout=5s --start-period=10s \
     CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:5000/health')"