feat(06-02): implement CSVFormatter with Unmask support

- Fixed 9-column header: id,provider,confidence,key,source,line,detected_at,verified,verify_status
- Uses encoding/csv for automatic quoting of commas/quotes in source paths
- Honors Options.Unmask for key column
- Registers under "csv" in output registry

pkg/output/csv.go

@@ -0,0 +1,60 @@
+package output
+
+import (
+	"encoding/csv"
+	"io"
+	"strconv"
+	"time"
+
+	"github.com/salvacybersec/keyhunter/pkg/engine"
+)
+
+func init() {
+	Register("csv", CSVFormatter{})
+}
+
+// CSVFormatter renders findings as comma-separated values with a fixed
+// header row. The id column is the zero-based index of the finding within
+// the slice -- the storage-layer rowid is intentionally not used here so
+// the formatter can run against in-memory results from a scan that has
+// not been persisted yet. Standard encoding/csv quoting rules apply, so
+// fields containing commas, quotes, or newlines are escaped automatically.
+type CSVFormatter struct{}
+
+// csvHeader is the exact, ordered header row written before any findings.
+// Column order must remain stable: downstream consumers may parse by index.
+// Columns: id, provider, confidence, key, source, line, detected_at, verified, verify_status
+var csvHeader = []string{
+	"id", "provider", "confidence", "key", "source",
+	"line", "detected_at", "verified", "verify_status",
+}
+
+// Format implements the Formatter interface.
+func (CSVFormatter) Format(findings []engine.Finding, w io.Writer, opts Options) error {
+	cw := csv.NewWriter(w)
+	if err := cw.Write(csvHeader); err != nil {
+		return err
+	}
+	for i, f := range findings {
+		key := f.KeyMasked
+		if opts.Unmask {
+			key = f.KeyValue
+		}
+		row := []string{
+			strconv.Itoa(i),
+			f.ProviderName,
+			f.Confidence,
+			key,
+			f.Source,
+			strconv.Itoa(f.LineNumber),
+			f.DetectedAt.Format(time.RFC3339),
+			strconv.FormatBool(f.Verified),
+			f.VerifyStatus,
+		}
+		if err := cw.Write(row); err != nil {
+			return err
+		}
+	}
+	cw.Flush()
+	return cw.Error()
+}