Initial MVP commit

internal/platform/timeparse/parse.go

@@ -0,0 +1,30 @@
+package timeparse
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"gitea.maximumdirect.net/ejr/weatherapi/internal/platform/constants"
+)
+
+func ParseTimestamp(raw string) (time.Time, error) {
+	raw = strings.TrimSpace(raw)
+	if raw == "" {
+		return time.Time{}, fmt.Errorf("timestamp is required")
+	}
+
+	var lastErr error
+	for _, layout := range constants.SupportedTimestampLayouts {
+		ts, err := time.Parse(layout, raw)
+		if err == nil {
+			return ts, nil
+		}
+		lastErr = err
+	}
+
+	if lastErr == nil {
+		lastErr = fmt.Errorf("invalid timestamp")
+	}
+	return time.Time{}, fmt.Errorf("timestamp must be RFC3339 (example: 2026-03-17T12:30:00Z): %w", lastErr)
+}