feat(ai): anonymous AI assistant on public shares

Lets an unauthenticated viewer of a published share ask an AI scoped strictly
to that share's page tree. The authenticated agent is untouched; the security
boundary is the tool scope (no identity), and nothing is persisted.

Server:
- workspace toggle settings.ai.publicShareAssistant (default off) +
  optional settings.ai.provider.publicShareChatModel (cheap model id; reuses
  the chat driver/baseUrl/key). getChatModel(workspaceId, override) substitutes
  only the model id, falling back to chatModel.
- POST /api/shares/ai/stream (@Public, SSE). Guardrail funnel, each failing
  before streaming: toggle off -> 404; share missing/wrong-workspace/sharing
  off -> 404; pageId not in share tree -> 404; provider unconfigured -> 503;
  per-IP (5/min) and per-workspace (300/h, IP-independent) rate limits -> 429.
  Uniform 404s never confirm a private page's existence.
- forShare read-only in-process toolset: searchSharePages (existing shareId
  FTS branch, no spaceId/userId), getSharePage (getShareForPage gate +
  share.id check, content via the public sanitizer), listSharePages. No write/
  comment/history/cross-space/external-MCP tools.
- Locked share system prompt + immutable safety block; stepCountIs(5).
- /shares/page-info exposes an aiAssistant flag (gated behind isSharingAllowed).

Client: an ephemeral, text-only Ask-AI widget on the public shared page,
shown only when the flag is set; useChat -> /api/shares/ai/stream,
credentials omit. Admin toggle + model field in Settings -> AI.

Also adds a jest moduleNameMapper for src/-rooted imports (fixes pre-existing
unresolvable specs; additive).

Implements docs/public-share-assistant-plan.md.

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

apps/server/src/core/workspace/dto/update-workspace.dto.ts

@@ -53,6 +53,10 @@ export class UpdateWorkspaceDto extends PartialType(CreateWorkspaceDto) {
   @IsBoolean()
   aiDictation: boolean;
 
+  @IsOptional()
+  @IsBoolean()
+  aiPublicShareAssistant: boolean;
+
   @IsOptional()
   @IsInt()
   @Min(1)

apps/server/src/core/workspace/services/workspace.service.ts

@@ -511,6 +511,21 @@ export class WorkspaceService {
         );
       }
 
+      if (typeof updateWorkspaceDto.aiPublicShareAssistant !== 'undefined') {
+        const prev = settingsBefore?.ai?.publicShareAssistant ?? false;
+        if (prev !== updateWorkspaceDto.aiPublicShareAssistant) {
+          before.aiPublicShareAssistant = prev;
+          after.aiPublicShareAssistant =
+            updateWorkspaceDto.aiPublicShareAssistant;
+        }
+        await this.workspaceRepo.updateAiSettings(
+          workspaceId,
+          'publicShareAssistant',
+          updateWorkspaceDto.aiPublicShareAssistant,
+          trx,
+        );
+      }
+
       delete updateWorkspaceDto.restrictApiToAdmins;
       delete updateWorkspaceDto.aiSearch;
       delete updateWorkspaceDto.generativeAi;
@@ -519,6 +534,7 @@ export class WorkspaceService {
       delete updateWorkspaceDto.allowMemberTemplates;
       delete updateWorkspaceDto.aiChat;
       delete updateWorkspaceDto.aiDictation;
+      delete updateWorkspaceDto.aiPublicShareAssistant;
 
       await this.workspaceRepo.updateWorkspace(
         updateWorkspaceDto,