email: group messages into conversations (Gmail-style threading)

Hybrid grouping via a new thread_id column: new mail threads exactly on
References/In-Reply-To (id is sha1(Message-Id), so a referenced id hashes to
the ancestor's own id); already-synced mail is backfilled with a
normalized-subject + counterpart key. Folder views collapse to one row per
thread with a count badge; the reader shows the thread as a collapsible stack.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/workspaces/types/email.ts

@@ -9,6 +9,9 @@ export type EmailSummary = {
   read?: boolean;
   fromDomain?: string;
   labels?: string[];
+  // Conversation grouping: total messages in the thread, and how many are unread (folder view only).
+  threadCount?: number;
+  threadUnread?: number;
 };
 
 export type EmailMessage = EmailSummary & {
@@ -17,3 +20,10 @@ export type EmailMessage = EmailSummary & {
   text?: string;
   attachments: Array<{ filename: string; size: number; contentType: string }>;
 };
+
+// A full conversation: every non-deleted message in the thread, oldest first.
+export type EmailThread = {
+  id: string; // the representative message id used to open the thread
+  subject: string;
+  messages: EmailMessage[];
+};

src/workspaces/types/index.ts

@@ -2,7 +2,7 @@ export type {} from './globals';
 export * from 'officerdb/types';
 
 export type { Job, JobStep, JobStatus, JobStepStatus, JobProgress } from './queue';
-export type { EmailSummary, EmailMessage } from './email';
+export type { EmailSummary, EmailMessage, EmailThread } from './email';
 
 export type SelectOption = { value: number | string; label?: string; href?: string };