fix(email): make the "Move to" context menu work across accounts

Moving a message to a folder in another account (own ↔ delegated/shared) via the
"Move to" context menu was a no-op — the handlers always issued a single-account
Email/set, which can't move between JMAP accounts. Drag-and-drop already routed
these correctly; the context menu never did.

Add moveToMailboxCrossAware: it detects a cross-account destination (own and
shared mailboxes both carry accountId) and routes through the drag-and-drop
crossAccountMoveEmails pipeline, else falls back to the single-account move.

Fix the pipeline for delegated folders too: a client can't stage a blob in a
delegated account (Blob/upload → blobNotFound), so importing into a shared folder
failed. When one client reaches both accounts, use a server-side JMAP Email/copy
(+ destroy original) instead of blob copy+import; the blob path is kept only for
separate cross-server login accounts. Adds client.copyEmailAcrossAccounts.

Unit tests for the dispatch; the two 08-shared-moves specs are un-pinned. Full
docker integration suite green (37 passed).

lib/demo/demo-client.ts

@@ -1094,6 +1094,7 @@ export class DemoJMAPClient implements IJMAPClient {
   // ── S/MIME raw-email helpers ──────────────────────────────────
 
   async importRawEmail(): Promise<string> { return generateDemoId('email'); }
+  async copyEmailAcrossAccounts(): Promise<string> { return generateDemoId('email'); }
   async submitEmail(): Promise<void> { /* no-op */ }
   async submitRawEmail(blob: Blob,
     identityId: string,

lib/jmap/client-interface.ts

@@ -345,4 +345,12 @@ export interface IJMAPClient {
   // ── S/MIME raw-email helpers ──────────────────────────────────
   importRawEmail(blob: Blob, mailboxIds: Record<string, boolean>, keywords?: Record<string, boolean>, accountId?: string): Promise<string>;
   submitEmail(emailId: string, identityId: string): Promise<void>;
+  /**
+   * Server-side move of one email across accounts reachable through THIS client
+   * (JMAP `Email/copy` + destroy-original). Used for delegated/shared folders,
+   * where the two accounts share a client but a client can't stage a blob in a
+   * delegated account (so the blob copy+import path doesn't work). Returns the
+   * new email id in the destination account.
+   */
+  copyEmailAcrossAccounts(emailId: string, fromAccountId: string, toAccountId: string, destMailboxId: string): Promise<string>;
 }

lib/jmap/client.ts

@@ -6394,6 +6394,32 @@ export class JMAPClient implements IJMAPClient {
    * a shared mailbox owned by another user). When omitted, falls back to the
    * client's own primary account.
    */
+  async copyEmailAcrossAccounts(
+    emailId: string,
+    fromAccountId: string,
+    toAccountId: string,
+    destMailboxId: string,
+  ): Promise<string> {
+    const response = await this.request([
+      ["Email/copy", {
+        fromAccountId,
+        accountId: toAccountId,
+        create: { c: { id: emailId, mailboxIds: { [destMailboxId]: true } } },
+        onSuccessDestroyOriginal: true,
+      }, "0"],
+    ]);
+    const res = response.methodResponses?.[0]?.[1];
+    const err = res?.notCreated?.c;
+    if (err) {
+      throw new Error(err.description || err.type || "Failed to copy email across accounts");
+    }
+    const id = res?.created?.c?.id;
+    if (!id) {
+      throw new Error("Email/copy succeeded but no ID returned");
+    }
+    return id;
+  }
+
   async importRawEmail(
     blob: Blob,
     mailboxIds: Record<string, boolean>,