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/rules/types.go

@@ -38,4 +38,4 @@ func (r RuleResult) WithMetadata(key, value string) RuleResult {
 type Rule interface {
 	Name() string
 	Evaluate(ctx EmailContext) RuleResult
-}
+}