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/workspace-cache-storage/workspace-cache-storage.service.ts

@@ -17,6 +17,7 @@ export const METADATA_VERSIONED_WORKSPACE_CACHE_KEY = {
   MetadataObjectMetadataMaps: 'metadata:object-metadata-maps',
   GraphQLUsedScalarNames: 'graphql:used-scalar-names',
   ORMEntitySchemas: 'orm:entity-schemas',
+  ToolCatalog: 'tool-catalog',
 } as const;
 export const WORKSPACE_CACHE_KEYS = {
   GraphQLOperations: 'graphql:operations',
@@ -202,6 +203,24 @@ export class WorkspaceCacheStorageService {
     );
   }
 
+  setToolCatalog(
+    cacheKey: string,
+    descriptors: unknown[],
+    ttl: number,
+  ): Promise<void> {
+    return this.cacheStorageService.set<unknown[]>(
+      `${METADATA_VERSIONED_WORKSPACE_CACHE_KEY.ToolCatalog}:${cacheKey}`,
+      descriptors,
+      ttl,
+    );
+  }
+
+  getToolCatalog(cacheKey: string): Promise<unknown[] | undefined> {
+    return this.cacheStorageService.get<unknown[]>(
+      `${METADATA_VERSIONED_WORKSPACE_CACHE_KEY.ToolCatalog}:${cacheKey}`,
+    );
+  }
+
   async flush(workspaceId: string, metadataVersion?: number): Promise<void> {
     await this.flushVersionedMetadata(workspaceId, metadataVersion);