feat: remove TimescaleDB, dead PG stores, and storage feature flags

Complete the ClickHouse migration by removing all PostgreSQL analytics
code. PostgreSQL now serves only RBAC, config, and audit — all
observability data is exclusively in ClickHouse.

- Delete 6 dead PostgreSQL store classes (executions, stats, diagrams,
  events, metrics, metrics-query) and 2 integration tests
- Delete RetentionScheduler (ClickHouse TTL handles retention)
- Remove all 7 cameleer.storage.* feature flags from application.yml
- Remove all @ConditionalOnProperty from ClickHouse beans in StorageBeanConfig
- Consolidate 14 Flyway migrations (V1-V14) into single clean V1 with
  only RBAC/config/audit tables (no TimescaleDB, no analytics tables)
- Switch from timescale/timescaledb-ha:pg16 to postgres:16 everywhere
  (docker-compose, deploy/postgres.yaml, test containers)
- Remove TimescaleDB check and /metrics-pipeline from DatabaseAdminController
- Set clickhouse.enabled default to true

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

deploy/postgres.yaml

@@ -16,7 +16,7 @@ spec:
     spec:
       containers:
         - name: postgres
-          image: timescale/timescaledb-ha:pg16
+          image: postgres:16
           ports:
             - containerPort: 5432
               name: postgres