feat(web): emailgen events in Orchestrator page

The SSE pipe at /orchestrator/events/stream was already streaming
'orchestrator.email.{decky_uuid}' events (the subscription is for the
'orchestrator.>' wildcard), but the consumer side dropped them on the
floor.  Three fixes to close the loop:

* useOrchestratorStream.ts now registers an 'email' SSE listener — the
  EventSource silently ignores frames whose event name has no listener,
  so missing this entry meant every email frame was dropped before
  reaching the page's onEvent handler.

* /api/v1/orchestrator/events accepts kind=email and dispatches to
  list_orchestrator_emails, adapting rows to the existing wire shape:
  subject -> action, sender_email -> src_decky_uuid, recipient_email
  -> dst_decky_uuid, plus email-specific extras (thread_id, language,
  mail_decky_uuid, message_id, in_reply_to) ride along as top-level
  keys.

* Orchestrator.tsx gains an 'email' tab in the kind filter and a
  branch in the row renderer / inspector that:
   - shows full sender / recipient (no UUID truncation),
   - chips the language code next to the subject,
   - relabels ACTION as SUBJECT in the inspector and surfaces
     thread / in-reply-to / mail-decky details.

The 'all' tab continues to show traffic+file only (today's behavior);
operators see emails by switching to the email tab.  A union view at
the API layer is the obvious follow-up but not necessary for now.

decnet_web/src/components/useOrchestratorStream.ts

@@ -5,7 +5,11 @@
  */
 import { useEffect, useRef } from 'react';
 
-export type OrchestratorStreamEventName = 'snapshot' | 'traffic' | 'file';
+export type OrchestratorStreamEventName =
+  | 'snapshot'
+  | 'traffic'
+  | 'file'
+  | 'email';
 
 export interface OrchestratorStreamEvent {
   name: OrchestratorStreamEventName | string;
@@ -21,7 +25,13 @@ export interface UseOrchestratorStreamOptions {
   onStatus?: (status: 'connecting' | 'live' | 'error') => void;
 }
 
-const NAMED_EVENTS: OrchestratorStreamEventName[] = ['snapshot', 'traffic', 'file'];
+// Must include every leaf the SSE endpoint emits — the EventSource
+// silently drops frames whose `event:` name has no listener registered.
+// New leaves on the bus need a corresponding entry here or the
+// dashboard ignores them despite the SSE pipe carrying them through.
+const NAMED_EVENTS: OrchestratorStreamEventName[] = [
+  'snapshot', 'traffic', 'file', 'email',
+];
 
 export function useOrchestratorStream({
   enabled,