fix(core): Resolve TypeScript strict mode and ES client API compatibility issues for v3.0.0

- Fix ES client v8+ API: use document/doc instead of body for index/update operations
- Add type assertions (as any) for ES client ILM, template, and search APIs
- Fix strict null checks with proper undefined handling (nullish coalescing)
- Fix MetricsCollector interface to match required method signatures
- Fix Logger.error signature compatibility in plugins
- Resolve TermsQuery type index signature conflict
- Remove sourceMap from tsconfig (handled by tsbuild with inlineSourceMap)

ts/core/connection/connection-manager.ts

@@ -1,6 +1,7 @@
 import { Client as ElasticClient } from '@elastic/elasticsearch';
-import { ElasticsearchConfig } from '../config/types.js';
-import { HealthChecker, HealthCheckResult, HealthStatus } from './health-check.js';
+import type { ElasticsearchConfig } from '../config/types.js';
+import { HealthChecker, HealthStatus } from './health-check.js';
+import type { HealthCheckResult } from './health-check.js';
 import { CircuitBreaker } from './circuit-breaker.js';
 import { Logger, defaultLogger } from '../observability/logger.js';
 import { MetricsCollector, defaultMetricsCollector } from '../observability/metrics.js';