feat: implement skills system for AI agents (#16865)

## Summary
This PR introduces a Skills system for AI agents, inspired by the [Agent
Skills specification](https://agentskills.io/specification).

## Changes

### Backend
- **SkillEntity**: New database entity with migration for storing skills
- **V2 Sync Mechanism**: Implemented FlatSkill, builders, validators,
and action handlers following the v2 flat entity pattern
- **Standard Skills**: Pre-defined skills (workflow-building,
data-manipulation, dashboard-building, metadata-building, research,
code-interpreter, xlsx, pdf, docx, pptx)
- **GraphQL API**: CRUD operations for skills with proper guards and
permissions
- **Workspace Cache**: Integrated skills into the workspace cache system

### Frontend  
- **Skills Table**: Searchable table in AI settings showing all skills
- **Skill Form**: Create/edit page with Label (primary), Description,
and Content (markdown editor)
- **API Name**: Following existing patterns, name is derived from label
with advanced settings toggle for custom API names
- **Standard vs Custom**: Standard skills are read-only, custom skills
can be edited/deleted

## Key Design Decisions
- Skills are stored in the database (Salesforce-like approach) rather
than files
- Name is derived from Label by default (isLabelSyncedWithName pattern)
- Skills reference functions/files via @ mentions in markdown content
rather than explicit relations
- Standard skills are synced from code, custom skills are created via UI

## Screenshots
Skills table and form UI follow existing settings patterns.

## Testing
- [x] Lint passes
- [x] Typecheck passes
- [ ] CI tests

packages/twenty-front/src/modules/object-record/record-field/ui/form-types/components/FormAdvancedTextFieldInput.tsx

@@ -1,5 +1,8 @@
 import { AdvancedTextEditor } from '@/advanced-text-editor/components/AdvancedTextEditor';
-import { useAdvancedTextEditor } from '@/advanced-text-editor/hooks/useAdvancedTextEditor';
+import {
+  type AdvancedTextEditorContentType,
+  useAdvancedTextEditor,
+} from '@/advanced-text-editor/hooks/useAdvancedTextEditor';
 import { FormFieldInputContainer } from '@/object-record/record-field/ui/form-types/components/FormFieldInputContainer';
 import { type VariablePickerComponent } from '@/object-record/record-field/ui/form-types/types/VariablePickerComponent';
 import { InputErrorHelper } from '@/ui/input/components/InputErrorHelper';
@@ -86,6 +89,7 @@ type FormAdvancedTextFieldInputProps = {
   fullScreenBreadcrumbs?: BreadcrumbProps['links'];
   minHeight: number;
   maxWidth: number;
+  contentType?: AdvancedTextEditorContentType;
 };
 
 export const FormAdvancedTextFieldInput = ({
@@ -103,6 +107,7 @@ export const FormAdvancedTextFieldInput = ({
   fullScreenBreadcrumbs,
   minHeight,
   maxWidth,
+  contentType = 'json',
 }: FormAdvancedTextFieldInputProps) => {
   const instanceId = useId();
   const isMobile = useIsMobile();
@@ -119,9 +124,15 @@ export const FormAdvancedTextFieldInput = ({
       placeholder: placeholder,
       readonly,
       defaultValue,
+      contentType,
       onUpdate: (editor) => {
-        const jsonContent = editor.getJSON();
-        onChange(JSON.stringify(jsonContent));
+        if (contentType === 'markdown') {
+          // For markdown mode, output the HTML which preserves formatting
+          onChange(editor.getHTML());
+        } else {
+          const jsonContent = editor.getJSON();
+          onChange(JSON.stringify(jsonContent));
+        }
       },
       onFocus: () => {
         pushFocusItemToFocusStack({