Write Posts 12-13 (Storage Deep Dive, Backup Strategies), add diagrams

- Post 12: CSV internals (direct/redirected I/O), protocol architecture,
  tiering design, cost case for three-tier SAN vs VCF 9 vs Azure Local,
  CSV troubleshooting decision tree, performance baseline methodology
- Post 13: VSS/RCT architecture, Veeam/Commvault/Rubrik/HYCU/Azure Backup
  honest assessments, backup solution decision matrix, RPO/RTO framework
- Added csv-io-architecture.svg, csv-troubleshooting-tree.svg, backup-architecture.svg

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

Author: kristopherjturner