v3.4.1: Graph delta added lines carry distance (delta verification)

Correctness fix: graph delta ## added lines carry distance (Section 10.1)

• The graph delta ## added line now ends with a trailing distance field: @id kind qname score provenance distance. The prior form omitted distance, but pack_root (Section 10.2) hashes distance, so a consumer could not reconstruct the new snapshot and recompute pack_root to verify new_root (Section 10.4). Delta verification was therefore impossible to perform from the wire; it now works. This changes the ## added line's arity (five fields to six); no functioning delta consumer existed under the prior form, so nothing that worked is broken. removed lines are unchanged (a removal matches by identity alone).
• The graph-delta conformance fixtures are now real cross-SDK tests, not skipped: 001 (encode, gains the trailing 0), 002 (decode a delta wire, apply it to a base snapshot, and verify the recomputed pack_root equals new_root), and 003 (the same delta with a wrong new_root, rejected with root_mismatch). Fixture 003 gained a base_snapshot so it can be applied.
• All six SDKs implement the graph delta path end to end (encode with distance, wire decode, and verify) and pass these fixtures byte-for-byte / hash-for-hash.