feat: wire external rules pipeline into ingress and dispatch

- Add DispatchContext field to Task model for rule metadata storage
- Add BlocklistEmails config (BLOCKLIST_EMAILS env var)
- Wire rules.Pipeline into IMAPWatcher, replacing inline whitelist check
- Pass rule metadata through DispatchContext to OpenClaw dispatch
- Remove isWhitelisted method (now handled by WhitelistRule)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/config/config.go

@@ -31,6 +31,7 @@ type Config struct {
 	BridgeCallbackToken string
 	SystemEmail         string
 	WhitelistEmails     []string
+	BlocklistEmails     []string
 
 	// Optional
 	IMAPProxyURL string
@@ -74,6 +75,14 @@ func Load() (*Config, error) {
 		}
 	}
 
+	if raw := os.Getenv("BLOCKLIST_EMAILS"); raw != "" {
+		for _, email := range strings.Split(raw, ",") {
+			if trimmed := strings.TrimSpace(email); trimmed != "" {
+				cfg.BlocklistEmails = append(cfg.BlocklistEmails, trimmed)
+			}
+		}
+	}
+
 	if cfg.ListenAddr == "" {
 		cfg.ListenAddr = ":8080"
 	}