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/pipeline_test.go

@@ -95,12 +95,12 @@ type stubRule struct {
 	result RuleResult
 }
 
-func (s *stubRule) Name() string                  { return s.name }
+func (s *stubRule) Name() string                       { return s.name }
 func (s *stubRule) Evaluate(_ EmailContext) RuleResult { return s.result }
 
 type trackingRule struct {
 	called bool
 }
 
-func (t *trackingRule) Name() string                  { return "tracker" }
-func (t *trackingRule) Evaluate(_ EmailContext) RuleResult { t.called = true; return Accept() }
+func (t *trackingRule) Name() string                       { return "tracker" }
+func (t *trackingRule) Evaluate(_ EmailContext) RuleResult { t.called = true; return Accept() }