feat: observability, IP filtering, stdout/clickhouse fixes (v1.1.11)

- feat(observability): metrics server with /metrics and /health endpoints
- feat(observability): correlation metrics (events, success/failed, reasons, buffers)
- feat(correlation): IP exclusion filter (exact IPs and CIDR ranges)
- feat(correlation): pending orphan delay for late-arriving B events
- fix(stdout): sink is now a no-op for data; JSON must never appear on stdout
- fix(clickhouse): all flush errors were silently discarded, now properly logged
- fix(clickhouse): buffer overflow with DropOnOverflow now logged at WARN
- fix(clickhouse): retry attempts logged at WARN with attempt/delay/error context
- feat(clickhouse): connection success logged at INFO, batch sends at DEBUG
- feat(clickhouse): SetLogger() for external logger injection
- test(stdout): assert stdout remains empty for correlated and orphan logs
- chore(rpm): bump version to 1.1.11, update changelog
- docs: README and architecture.yml updated

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

internal/adapters/outbound/clickhouse/sink.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/ClickHouse/clickhouse-go/v2"
 	"github.com/logcorrelator/logcorrelator/internal/domain"
+	"github.com/logcorrelator/logcorrelator/internal/observability"
 )
 
 const (
@@ -53,6 +54,12 @@ type ClickHouseSink struct {
 	done      chan struct{}
 	wg        sync.WaitGroup
 	closeOnce sync.Once
+	logger    *observability.Logger
+}
+
+// SetLogger sets the logger used by the sink.
+func (s *ClickHouseSink) SetLogger(logger *observability.Logger) {
+	s.logger = logger.WithFields(map[string]any{"sink": "clickhouse"})
 }
 
 // NewClickHouseSink creates a new ClickHouse sink.
@@ -83,6 +90,7 @@ func NewClickHouseSink(config Config) (*ClickHouseSink, error) {
 		buffer:    make([]domain.CorrelatedLog, 0, config.BatchSize),
 		flushChan: make(chan struct{}, 1),
 		done:      make(chan struct{}),
+		logger:    observability.NewLogger("clickhouse"),
 	}
 
 	// Parse DSN and create options
@@ -107,6 +115,8 @@ func NewClickHouseSink(config Config) (*ClickHouseSink, error) {
 	}
 
 	s.conn = conn
+	s.log().Infof("connected to ClickHouse: table=%s batch_size=%d flush_interval_ms=%d",
+		config.Table, config.BatchSize, config.FlushIntervalMs)
 
 	// Start flush goroutine
 	s.wg.Add(1)
@@ -120,6 +130,14 @@ func (s *ClickHouseSink) Name() string {
 	return "clickhouse"
 }
 
+// log returns the logger, initializing a default one if not set (e.g. in tests).
+func (s *ClickHouseSink) log() *observability.Logger {
+	if s.logger == nil {
+		s.logger = observability.NewLogger("clickhouse")
+	}
+	return s.logger
+}
+
 // Reopen is a no-op for ClickHouse (connection is managed internally).
 func (s *ClickHouseSink) Reopen() error {
 	return nil
@@ -146,6 +164,7 @@ func (s *ClickHouseSink) Write(ctx context.Context, log domain.CorrelatedLog) er
 		s.mu.Unlock()
 
 		if drop {
+			s.log().Warnf("buffer full, dropping log: table=%s buffer_size=%d", s.config.Table, s.config.MaxBufferSize)
 			return nil
 		}
 		if time.Now().After(deadline) {
@@ -201,7 +220,9 @@ func (s *ClickHouseSink) flushLoop() {
 		select {
 		case <-s.done:
 			ctx, cancel := context.WithTimeout(context.Background(), time.Duration(s.config.TimeoutMs)*time.Millisecond)
-			_ = s.doFlush(ctx)
+			if err := s.doFlush(ctx); err != nil {
+				s.log().Error("final flush on close failed", err)
+			}
 			cancel()
 			return
 
@@ -212,7 +233,9 @@ func (s *ClickHouseSink) flushLoop() {
 
 			if needsFlush {
 				ctx, cancel := context.WithTimeout(context.Background(), time.Duration(s.config.TimeoutMs)*time.Millisecond)
-				_ = s.doFlush(ctx)
+				if err := s.doFlush(ctx); err != nil {
+					s.log().Error("periodic flush failed", err)
+				}
 				cancel()
 			}
 
@@ -223,7 +246,9 @@ func (s *ClickHouseSink) flushLoop() {
 
 			if needsFlush {
 				ctx, cancel := context.WithTimeout(context.Background(), time.Duration(s.config.TimeoutMs)*time.Millisecond)
-				_ = s.doFlush(ctx)
+				if err := s.doFlush(ctx); err != nil {
+					s.log().Error("batch flush failed", err)
+				}
 				cancel()
 			}
 		}
@@ -247,7 +272,6 @@ func (s *ClickHouseSink) doFlush(ctx context.Context) error {
 		return fmt.Errorf("clickhouse connection is not initialized")
 	}
 
-	// Log batch info before sending
 	batchSize := len(buffer)
 
 	// Retry logic with exponential backoff
@@ -255,6 +279,8 @@ func (s *ClickHouseSink) doFlush(ctx context.Context) error {
 	for attempt := 0; attempt < MaxRetries; attempt++ {
 		if attempt > 0 {
 			delay := RetryBaseDelay * time.Duration(1<<uint(attempt-1))
+			s.log().Warnf("retrying batch insert: attempt=%d/%d delay=%s rows=%d err=%v",
+				attempt+1, MaxRetries, delay, batchSize, lastErr)
 			select {
 			case <-time.After(delay):
 			case <-ctx.Done():
@@ -264,6 +290,7 @@ func (s *ClickHouseSink) doFlush(ctx context.Context) error {
 
 		lastErr = s.executeBatch(ctx, buffer)
 		if lastErr == nil {
+			s.log().Debugf("batch sent: rows=%d table=%s", batchSize, s.config.Table)
 			return nil
 		}