Add unit and e2e tests covering the remaining Section 18 scenarios:

Unit tests (32 new):
- Quorum: #4 fail→abandoned, #16 timeout→inconclusive, #27 single-round
  dual-evidence, #28 dynamic threshold undersized, #33 batched per-key,
  #34 partial response unresolved, #42 quorum-derived paid-list auth
- Admission: #5 unauthorized peer, #7 out-of-range rejected
- Config: #18 invalid config rejected, #26 dynamic paid threshold
- Scheduling: #8 dedup safety, #8 replica/paid collapse
- Neighbor sync: #35 round-robin cooldown skip, #36 cycle completion,
  #38 snapshot stability mid-join, #39 unreachable removal + slot fill,
  #40 cooldown peer removed, #41 cycle termination guarantee,
  consecutive rounds, cycle preserves sync times
- Pruning: #50 hysteresis prevents premature delete, #51 timestamp reset
  on heal, #52 paid/record timestamps independent, #23 entry removal
- Audit: #19/#53 partial failure mixed responsibility, #54 all pass,
  #55 empty failure discard, #56 repair opportunity filter,
  response count validation, digest uses full record bytes
- Types: #13 bootstrap drain, repair opportunity edge cases,
  terminal state variants
- Bootstrap claims: #46 first-seen recorded, #49 cleared on normal

E2e tests (4 new):
- #2 fresh offer with empty PoP rejected
- #5/#37 neighbor sync request returns response
- #11 audit challenge multi-key (present + absent)
- Fetch not-found for non-existent key

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

Add unit and e2e tests covering the remaining Section 18 scenarios:

Unit tests (32 new):
- Quorum: #4 fail→abandoned, #16 timeout→inconclusive, #27 single-round
  dual-evidence, #28 dynamic threshold undersized, #33 batched per-key,
  #34 partial response unresolved, #42 quorum-derived paid-list auth
- Admission: #5 unauthorized peer, #7 out-of-range rejected
- Config: #18 invalid config rejected, #26 dynamic paid threshold
- Scheduling: #8 dedup safety, #8 replica/paid collapse
- Neighbor sync: #35 round-robin cooldown skip, #36 cycle completion,
  #38 snapshot stability mid-join, #39 unreachable removal + slot fill,
  #40 cooldown peer removed, #41 cycle termination guarantee,
  consecutive rounds, cycle preserves sync times
- Pruning: #50 hysteresis prevents premature delete, #51 timestamp reset
  on heal, #52 paid/record timestamps independent, #23 entry removal
- Audit: #19/#53 partial failure mixed responsibility, #54 all pass,
  #55 empty failure discard, #56 repair opportunity filter,
  response count validation, digest uses full record bytes
- Types: #13 bootstrap drain, repair opportunity edge cases,
  terminal state variants
- Bootstrap claims: #46 first-seen recorded, #49 cleared on normal

E2e tests (4 new):
- #2 fresh offer with empty PoP rejected
- #5/#37 neighbor sync request returns response
- #11 audit challenge multi-key (present + absent)
- Fetch not-found for non-existent key

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