feat: follow an epic with everything under it

«Seguir todo» on a ticket with subtasks (and on each epic of the Epics
page) tells you of it and of every ticket hanging from it, at any depth,
also the ones added later: their moves, assignments, comments and plan
changes, as a follower of each, plus when a ticket is placed under it.
Guests of a private project are left out. Personal, no history (Mongo
`tree_follows`).

API: followTree / unfollowTree, Issue.followingTree, PUT/DELETE
/api/issues/{issue}/follow-tree. MCP: watch_issue with tree.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/mcp/src/app/tools/issues.resolver.ts

@@ -565,19 +565,29 @@ export class IssuesResolver {
   @Tool({
     name: 'watch_issue',
     description:
-      'Follow a ticket (notifications of its changes and comments) or stop following it.',
+      'Follow a ticket (notifications of its changes and comments) or stop following it. With tree: true, an epic (or any ticket with subtasks) with everything under it, also tickets added later.',
     paramsSchema: z.object({
       issue: issueRef,
       follow: z.boolean().default(true),
+      tree: z.boolean().default(false),
     }),
     annotations: { ...WRITE, idempotentHint: true },
   })
   watch(
-    { issue, follow }: { issue: string; follow: boolean },
+    { issue, follow, tree }: { issue: string; follow: boolean; tree: boolean },
     ctx: McpContext,
   ) {
     const client = this.api.as(ctx);
     const options = { params: { path: { issue } } };
+    if (tree)
+      return toolResult(async () => {
+        await this.api.data(
+          follow
+            ? client.PUT('/api/issues/{issue}/follow-tree', options)
+            : client.DELETE('/api/issues/{issue}/follow-tree', options),
+        );
+        return { issue, followingTree: follow };
+      });
     return toolResult(() =>
       this.api.data(
         follow