feat: improve AI chat - system prompt, tool output, context window display (#17769)

⚠️ **AI-generated PR — not ready for review** ⚠️

cc @FelixMalfait

---

## Changes

### System prompt improvements
- Explicit skill-before-tools workflow to prevent the model from calling
tools without loading the matching skill first
- Data efficiency guidance (default small limits, use filters)
- Pluralized `load_skill` → `load_skills` for consistency with
`load_tools`

### Token usage reduction
- Output serialization layer: strips null/undefined/empty values from
tool results
- Lowered default `find_*` limit from 100 → 10, max from 1000 → 100

### System object tool generation
- System objects (calendar events, messages, etc.) now generate AI tools
- Only workflow-related and favorite-related objects are excluded

### Context window display fix
- **Bug**: UI compared cumulative tokens (sum of all turns) against
single-request context window → showed 100% after a few turns
- **Fix**: Track `conversationSize` (last step's `inputTokens`) which
represents the actual conversation history size sent to the model
- New `conversationSize` column on thread entity with migration

### Workspace AI instructions
- Support for custom workspace-level AI instructions

---------

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>

packages/twenty-server/src/engine/metadata-modules/ai/ai-agent-execution/services/agent-actor-context.service.ts

@@ -12,11 +12,19 @@ import { UserRoleService } from 'src/engine/metadata-modules/user-role/user-role
 import { GlobalWorkspaceOrmManager } from 'src/engine/twenty-orm/global-workspace-datasource/global-workspace-orm.manager';
 import { buildSystemAuthContext } from 'src/engine/twenty-orm/utils/build-system-auth-context.util';
 
+export type UserContext = {
+  firstName: string;
+  lastName: string;
+  locale: string;
+  timezone: string | null;
+};
+
 export type AgentActorContext = {
   actorContext: ActorMetadata;
   roleId: string;
   userId: string;
   userWorkspaceId: string;
+  userContext: UserContext;
 };
 
 @Injectable()
@@ -87,11 +95,19 @@ export class AgentActorContextService {
       workspaceMemberId: workspaceMember.id,
     });
 
+    const userContext: UserContext = {
+      firstName: workspaceMember.name?.firstName ?? '',
+      lastName: workspaceMember.name?.lastName ?? '',
+      locale: userWorkspace.locale,
+      timezone: workspaceMember.timeZone ?? null,
+    };
+
     return {
       actorContext,
       roleId,
       userId: userWorkspace.userId,
       userWorkspaceId,
+      userContext,
     };
   }
 }