refactor: extract SHA3 hashing utilities to utils/hash.go

- Move all SHA3-512 hashing functions to utils package
- Update import statements and function calls
- Maintain zero functional changes
- First step in systematic main.go refactoring

🤖 Generated with [Claude Code](https://claude.ai/code)

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

--help

@@ -0,0 +1,33 @@
+node_id: GALACTICA
+bind_address: 127.0.0.1
+port: 8080
+data_dir: ./data
+seed_nodes: []
+read_only: false
+log_level: info
+gossip_interval_min: 60
+gossip_interval_max: 120
+sync_interval: 300
+catchup_interval: 120
+bootstrap_max_age_hours: 720
+throttle_delay_ms: 100
+fetch_delay_ms: 50
+compression_enabled: true
+compression_level: 3
+default_ttl: "0"
+max_json_size: 1048576
+rate_limit_requests: 100
+rate_limit_window: 1m
+tamper_log_actions:
+    - data_write
+    - user_create
+    - auth_failure
+backup_enabled: true
+backup_schedule: 0 0 * * *
+backup_path: ./backups
+backup_retention: 7
+auth_enabled: true
+tamper_logging_enabled: true
+clustering_enabled: true
+rate_limiting_enabled: true
+revision_history_enabled: true