Add chlog CLI with chcat/chtail/chgrep entrypoints

Single Go binary for the ClickHouse log store (logs.raw): chlog with
cat/tail/grep subcommands, plus chcat/chtail/chgrep argv[0]-dispatched
symlink entrypoints. Every query is time-bounded and fully parameterized;
chgrep guards wide unfiltered scans. Ships nfpm RPM with completions and
woodpecker PR/tag pipelines mirroring node-lookup.

internal/chlog/tail.go

@@ -0,0 +1,84 @@
+package chlog
+
+import (
+	"context"
+	"time"
+)
+
+const (
+	TailInterval = 2 * time.Second
+	tailOverlap  = 5 * time.Second
+)
+
+// Tail streams the initial window then polls every interval. Each poll
+// re-queries from a little before the last-seen timestamp and drops rows
+// already emitted, so late-arriving rows inside the overlap still surface.
+func Tail(ctx context.Context, c runner, f Filter, now func() time.Time, interval time.Duration, emit func(Row) error) error {
+	if now == nil {
+		now = time.Now
+	}
+	if interval <= 0 {
+		interval = TailInterval
+	}
+
+	seen := map[uint64]time.Time{}
+	lastTS := f.Since
+	track := func(r Row) error {
+		if ts := r.Time(); ts.After(lastTS) {
+			lastTS = ts
+		}
+		seen[r.Key()] = r.Time()
+		return emit(r)
+	}
+
+	first := f
+	first.Until = now().UTC()
+	first.Limit = 0
+	if _, err := Page(ctx, c, first, 0, track); err != nil {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+		return err
+	}
+
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-ticker.C:
+		}
+
+		since := lastTS.Add(-tailOverlap)
+		if since.Before(f.Since) {
+			since = f.Since
+		}
+		pf := f
+		pf.Since = since
+		pf.Until = now().UTC()
+		pf.Limit = 0
+		if !pf.Since.Before(pf.Until) {
+			continue
+		}
+		_, err := Page(ctx, c, pf, 0, func(r Row) error {
+			if _, dup := seen[r.Key()]; dup {
+				return nil
+			}
+			return track(r)
+		})
+		if err != nil {
+			if ctx.Err() != nil {
+				return ctx.Err()
+			}
+			return err
+		}
+
+		floor := lastTS.Add(-2 * tailOverlap)
+		for k, ts := range seen {
+			if ts.Before(floor) {
+				delete(seen, k)
+			}
+		}
+	}
+}