feat(ai-chat): per-user AI agent backend — LLM config, read-only agent, provenance schema

WIP checkpoint of the gitmost AI-chat backend (plan stages A + B1 + B3a).
The agent acts under the requesting user's JWT (Docmost CASL enforces page
access); the external service-account /mcp endpoint is untouched.

LLM provider config (A2-A4):
- integrations/crypto: AES-256-GCM SecretBoxService (key derived from APP_SECRET,
  per-record salt/iv; clear error on rotation instead of crashing).
- ai_provider_credentials table/repo/types: encrypted API key stored outside
  workspace settings/baseFields, write-only (never returned by any endpoint).
- integrations/ai: per-workspace AI SDK v6 provider driver (openai/gemini/ollama),
  admin-gated GET(masked)/PATCH(write-only key)/Test endpoints; settings.ai.provider
  holds non-secret config incl. systemPrompt. Removed unused AI_* env getters (DB is
  the single source of truth).

Chat module (A1, A5-A8):
- ai_chats/ai_chat_messages repos (workspace-scoped, soft-delete, tsv never selected).
- core/ai-chat: CRUD + POST /ai-chat/stream (Fastify hijack + AI SDK v6
  pipeUIMessageStreamToResponse, abort on disconnect, persist user/assistant msgs).
- Agent loop: streamText + stepCountIs(8); read tools searchPages/getPage via a
  per-request DocmostClient over loopback REST under the user's minted access token.
- Gate settings.ai.chat (+ 503 when provider unconfigured); buildSystemPrompt with a
  non-removable safety/anti-prompt-injection framework. Per-user rate limit.

Per-user auth (B1):
- @docmost/mcp DocmostClient gains an additive getToken variant (carry a user JWT,
  re-fetch on 401) and exports DocmostClient; the email/password service-account path
  (external /mcp, stdio) is unchanged.

Agent-edit provenance backbone (B3a):
- Migration: pages/page_history (last_updated_source, last_updated_ai_chat_id) and
  comments (created_source, ai_chat_id, resolved_source).
- Signed actor/aiChatId claim in the collab token; onAuthenticate propagates it,
  onStoreDocument writes it with a sticky agent marker, saveHistory copies it.

Migrations auto-run on boot (additive). Write tools, frontend, RAG and external MCP
servers are not in this checkpoint.

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

apps/server/src/database/repos/workspace/workspace.repo.ts

@@ -211,6 +211,36 @@ export class WorkspaceRepo {
       .executeTakeFirst();
   }
 
+  /**
+   * Deep-merge a partial provider config into the fixed path
+   * `settings.ai.provider`. Unlike `updateAiSettings` (single scalar key under
+   * `settings.ai`), this stores a nested object. The path is constant — only the
+   * provider value is parameterized (bound, not `sql.raw`) — so it cannot store
+   * a secret and is safe from injection. Sibling `settings.ai.*` keys (search /
+   * generative / chat / mcp / systemPrompt) and provider fields absent from the
+   * partial are preserved via jsonb `||` merge.
+   */
+  async updateAiProviderSettings(
+    workspaceId: string,
+    provider: Record<string, unknown>,
+    trx?: KyselyTransaction,
+  ): Promise<Workspace> {
+    const db = dbOrTx(this.db, trx);
+    const providerJson = JSON.stringify(provider);
+    return db
+      .updateTable('workspaces')
+      .set({
+        settings: sql`COALESCE(settings, '{}'::jsonb)
+                || jsonb_build_object('ai', COALESCE(settings->'ai', '{}'::jsonb)
+                || jsonb_build_object('provider', COALESCE(settings->'ai'->'provider', '{}'::jsonb)
+                || ${providerJson}::jsonb))`,
+        updatedAt: new Date(),
+      })
+      .where('id', '=', workspaceId)
+      .returning(this.baseFields)
+      .executeTakeFirst();
+  }
+
   async updateSharingSettings(
     workspaceId: string,
     prefKey: string,