alpha1: strict replay clears full 8.22M-block local block_log with 0 errors

Major fixes:
- iter17: block-1 off-by-99 in CurrentAslot (closes the 5.21M cascade
  that included gxt-1080-sc-0028 disable, median feed at 5,210,400,
  martin-stuessy 91-sat shortfall).
- HBDPrintRate=0 was treated as 'unset' in payCreateHbd and fell back
  to 10000 (100% HBD); hived treats 0 as the post-HF14 0%-cap. Closes
  the cryptos 35,850-sat shortfall at block 6,198,475.

Performance:
- Genesis → 1M: ~103K blocks/s
- Cliff (3M → 4M): 10.2K blocks/s (was 2.0K pre-perf-cliff = 5.1×)
- 5M → 8M steady-state: 11–12K blocks/s
- Snapshot/Restore now O(1) via chainbase-style undo log instead of
  O(overlay-size) shallow copy (the cliff root cause).
- Multiple alloc reductions (commentKey 1-alloc, memIter zero-copy,
  WitnessStore + AccountStore object pooling, fcraw short-string
  interning, Session.Put buffer reuse).
- Native uint128 in funds reward math (replaces math/big.Int).
- WitnessStore Mutate + dirtyOrder + btree path hints.

Tooling:
- ghive-tools replay: --snapshot-every / --snapshot-dir periodic dir
  snapshots; --load-snapshot (file or dir auto-detect);
  --save-dir-snapshot-at / --save-dir-snapshot-to for exact-block dir
  snapshots; --cpuprofile / --memprofile.
- cmd/drift-hunter: per-block diff vs hived API across DGPO,
  witness_schedule, feed_history, reward_funds, per-witness top-N,
  per-account (--account=NAME).
- scripts/hived-at <BLOCK> dgpo|witness|account|schedule|raw|shell|stop:
  one-shot wrapper around the hived checkpoint framework, reuses
  prepared dirs, per-block port allocation, daemonized via setsid.

Replay status: 0 errors through end of local block_log (8,221,695).
Next divergence (if any) requires a longer block_log to find.