Reduce disk write amplification across cluster (~200-350 GB/day savings) [ci skip]

- Prometheus: persist metric whitelist (keep rules) to Helm template, preventing
  regression from 33K to 250K samples/scrape on next apply. Reduce retention 52w→26w.
- MySQL InnoDB: aggressive write reduction — flush_log_at_trx_commit=0, sync_binlog=0,
  doublewrite=OFF, io_capacity=100/200, redo_log=1GB, flush_neighbors=1, reduced page cleaners.
- etcd: increase snapshot-count 10000→50000 to reduce WAL snapshot frequency.
- VM disks: enable TRIM/discard passthrough to LVM thin pool via create-vm module.
- Cloud-init: enable fstrim.timer, journald limits (500M/7d/compress).
- Kubelet: containerLogMaxSize=10Mi, containerLogMaxFiles=3.
- Technitium: DNS query log retention 0→30 days (was unlimited writes to MySQL).

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

stacks/technitium/modules/technitium/main.tf

@@ -460,7 +460,7 @@ resource "kubernetes_cron_job_v1" "technitium_password_sync" {
                 set -e
                 TOKEN=$$(curl -sf "http://technitium-web:5380/api/user/login?user=$$TECH_USER&pass=$$TECH_PASS" | grep -o '"token":"[^"]*"' | cut -d'"' -f4)
                 if [ -z "$$TOKEN" ]; then echo "Login failed"; exit 1; fi
-                CONFIG="{\"enableLogging\":true,\"maxQueueSize\":1000000,\"maxLogDays\":0,\"maxLogRecords\":0,\"databaseName\":\"technitium\",\"connectionString\":\"Server=mysql.dbaas.svc.cluster.local; Port=3306; Uid=technitium; Pwd=$$DB_PASSWORD;\"}"
+                CONFIG="{\"enableLogging\":true,\"maxQueueSize\":1000000,\"maxLogDays\":30,\"maxLogRecords\":0,\"databaseName\":\"technitium\",\"connectionString\":\"Server=mysql.dbaas.svc.cluster.local; Port=3306; Uid=technitium; Pwd=$$DB_PASSWORD;\"}"
                 APP_NAME="Query Logs (MySQL)"
                 curl -sf -X POST "http://technitium-web:5380/api/apps/config/set?token=$$TOKEN" --data-urlencode "name=$$APP_NAME" --data-urlencode "config=$$CONFIG"
                 echo "Password sync complete"