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>

ui/src/pages/Admin/DatabaseAdminPage.tsx

@@ -37,7 +37,6 @@ export default function DatabaseAdminPage() {
       <div style={{ display: 'flex', gap: '1rem', marginBottom: '1.5rem', flexWrap: 'wrap' }}>
         <StatCard label="Status" value={unreachable ? 'Disconnected' : status ? 'Connected' : '\u2014'} accent={unreachable ? 'error' : status ? 'success' : undefined} />
         <StatCard label="Version" value={status?.version ?? '—'} />
-        <StatCard label="TimescaleDB" value={status?.timescaleDb ? 'Enabled' : 'Disabled'} />
       </div>
 
       {pool && (