fix: replace wall-clock timestamp dependency with VTS for block validation

The network was deadlocking because timestamp validation rejected valid
blocks — nodes couldn't reach 2/3 consensus and the chain stalled.

Key changes:
- Timestamp validation split into SYNC/LIVE modes: wall-clock checks
  disabled during sync, VTS (cryptographic hash chain) + prev_hash
  provide ordering guarantees without clock dependency
- Disk-first height ordering: all update_all_heights and rollback paths
  now write RocksDB before RAM to prevent crash-induced divergence
- O(1) hash index: microblock_hash_{height} in metadata CF enables
  prev_hash validation without loading full block body (WriteBatch atomic)
- 3-tier prev_hash validation: hash index → full block + backfill →
  MISSING_PREVIOUS self-healing (buffer & retry, not reject)
- VTS strict monotonicity: regression tolerance tightened from 15M to 5M
  hashes (30s → 10s), graceful skip when prev block unavailable
- Chronic stall recovery threshold reduced from 300s to 120s for faster
  PFP activation when consensus is stuck
- Periodic disk/RAM integrity check every 1000 blocks with auto-repair
- Hash index migration at startup (idempotent, non-fatal fallback)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: AIQnetLab