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-shared/src/utils/index.ts

@@ -145,6 +145,7 @@ export { safeParseRelativeDateFilterJSONStringified } from './safeParseRelativeD
 export { getGenericOperationName } from './sentry/getGenericOperationName';
 export { getHumanReadableNameFromCode } from './sentry/getHumanReadableNameFromCode';
 export { appendCopySuffix } from './strings/appendCopySuffix';
+export { camelToSnakeCase } from './strings/camelToSnakeCase';
 export { capitalize } from './strings/capitalize';
 export { pascalCase } from './strings/pascalCase';
 export { stringifySafely } from './strings/stringifySafely';

packages/twenty-shared/src/utils/strings/__tests__/camelToSnakeCase.test.ts

@@ -0,0 +1,25 @@
+import { camelToSnakeCase } from '../camelToSnakeCase';
+
+describe('camelToSnakeCase', () => {
+  it('should convert camelCase to snake_case', () => {
+    expect(camelToSnakeCase('cloudUserWorkspaces')).toBe(
+      'cloud_user_workspaces',
+    );
+  });
+
+  it('should convert single-word camelCase', () => {
+    expect(camelToSnakeCase('people')).toBe('people');
+  });
+
+  it('should handle two-word camelCase', () => {
+    expect(camelToSnakeCase('selfHostingUser')).toBe('self_hosting_user');
+  });
+
+  it('should handle already snake_case', () => {
+    expect(camelToSnakeCase('already_snake')).toBe('already_snake');
+  });
+
+  it('should handle single word', () => {
+    expect(camelToSnakeCase('company')).toBe('company');
+  });
+});

packages/twenty-shared/src/utils/strings/camelToSnakeCase.ts

@@ -0,0 +1,2 @@
+export const camelToSnakeCase = (str: string): string =>
+  str.replace(/[A-Z]/g, (letter) => `_${letter.toLowerCase()}`);