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>

HOWTO.md

@@ -27,7 +27,7 @@ Start PostgreSQL:
 docker compose up -d
 ```
 
-This starts TimescaleDB (PostgreSQL 16). The database schema is applied automatically via Flyway migrations on server startup. ClickHouse tables are created by the schema initializer on startup.
+This starts PostgreSQL 16. The database schema is applied automatically via Flyway migrations on server startup. ClickHouse tables are created by the schema initializer on startup.
 
 | Service    | Port | Purpose              |
 |------------|------|----------------------|