feat(ai-chat): show creation time and origin document in chat list

Each chat row in the AI-chat history now shows a dimmed second line with
how long ago the chat was created and the document it was created in
("N ago / <document>", or "No document" when started outside a page).

Server:
- New migration: nullable ai_chats.page_id (FK pages.id, ON DELETE SET NULL).
- Capture the origin page at chat creation from the client-supplied openPage,
  but validate it first: it must be a real page in the same workspace that the
  user may read (PageAccessService.validateCanView), else null. This keeps the
  "openPage.id is attacker-controllable but harmless" invariant - preventing a
  cross-workspace/cross-space page-title leak and a post-hijack FK crash.
- findByCreator left-joins pages (scoped by workspace, defense-in-depth) and
  returns pageTitle.

Client:
- IAiChat gains pageId/pageTitle; ConversationList renders a ChatMetaLine
  (useTimeAgo + origin document) as a dimmed second line.
- Add i18n key "No document" (en-US, ru-RU).

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

apps/server/src/database/migrations/20260622T120000-ai-chat-page-origin.ts

@@ -0,0 +1,18 @@
+import { type Kysely } from 'kysely';
+
+export async function up(db: Kysely<any>): Promise<void> {
+  // The document a chat was created in (the user's open page at first message).
+  // Informational provenance shown in the chat-history list. NULL => the chat
+  // was started outside any document. ON DELETE SET NULL: a hard-deleted page
+  // degrades the chat to "no document" instead of breaking it.
+  await db.schema
+    .alterTable('ai_chats')
+    .addColumn('page_id', 'uuid', (col) =>
+      col.references('pages.id').onDelete('set null'),
+    )
+    .execute();
+}
+
+export async function down(db: Kysely<any>): Promise<void> {
+  await db.schema.alterTable('ai_chats').dropColumn('page_id').execute();
+}

apps/server/src/database/repos/ai-chat/ai-chat.repo.ts

@@ -43,10 +43,21 @@ export class AiChatRepo {
           .on('aiAgentRoles.deletedAt', 'is', null)
           .on('aiAgentRoles.enabled', '=', true),
       )
+      // Left-join the origin page for its title (provenance shown in the list).
+      // Scoped to the chat's workspace as defense-in-depth so a page id can only
+      // ever surface a same-workspace title. No deletedAt filter: a soft-deleted
+      // page keeps showing its historical title; a hard-deleted page already
+      // nulls aiChats.pageId via the FK.
+      .leftJoin('pages', (join) =>
+        join
+          .onRef('pages.id', '=', 'aiChats.pageId')
+          .onRef('pages.workspaceId', '=', 'aiChats.workspaceId'),
+      )
       .selectAll('aiChats')
       .select([
         'aiAgentRoles.name as roleName',
         'aiAgentRoles.emoji as roleEmoji',
+        'pages.title as pageTitle',
       ])
       .where('aiChats.creatorId', '=', creatorId)
       .where('aiChats.workspaceId', '=', workspaceId)

apps/server/src/database/types/db.d.ts

@@ -575,6 +575,9 @@ export interface AiChats {
   // chat to universal instead of breaking it. Resolved from this column on every
   // turn — NOT from the request body.
   roleId: string | null;
+  // The document the chat was created in (open page at first message). NULL =>
+  // started outside any document. ON DELETE SET NULL on the page FK.
+  pageId: string | null;
   createdAt: Generated<Timestamp>;
   updatedAt: Generated<Timestamp>;
   deletedAt: Timestamp | null;