feat(iios): @mentions via inbox fan-out + my-annotations query (pins/saves)

Mentions ride the existing event-driven inbox — no chat parsing in the kernel:
- send() carries an OPAQUE mentions[] (userIds) into the message event; the kernel
  never parses "@". The app supplies the notify-list.
- InboxProjector fans out a MENTION inbox item (new generic inbox kind) to each
  mentioned *participant* (never the sender), idempotent per source message; reading
  the thread resolves the reader's MENTION + NEEDS_REPLY items to DONE.
- New MENTION value in the generic IiosInboxItemKind taxonomy (migration).

Pins/saves reuse the annotation primitive; new generic query powers a Saved list:
- MessageService.listMyAnnotated(principal, type) + GET /v1/threads/my-annotations
  returns the caller's annotated messages (type "save") with thread context.

Tests: 182 pass (+4: mention fan-out, resolve-on-read, saved query, opaque mentions).
Verified live: mention→inbox delivery, read→resolve, pin/save persistence.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/src/threads/threads.controller.ts

@@ -8,6 +8,7 @@ import {
   HttpCode,
   Param,
   Post,
+  Query,
 } from '@nestjs/common';
 import { ThreadsService } from './threads.service';
 import { MessageService } from '../messaging/message.service';
@@ -28,6 +29,12 @@ export class ThreadsController {
     return this.messages.listThreads(this.principal(auth));
   }
 
+  /** Generic "my annotated messages" (e.g. ?type=save for a personal bookmarks list). */
+  @Get('my-annotations')
+  async myAnnotations(@Headers('authorization') auth?: string, @Query('type') type = 'save') {
+    return this.messages.listMyAnnotated(this.principal(auth), type);
+  }
+
   /** Create a thread; `membership`/`creatorRole`/`subject` are opaque, app-supplied attributes the kernel stores but never interprets. */
   @Post()
   @HttpCode(201)