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/advanced-text-editor/hooks/useAdvancedTextEditor.ts

@@ -17,9 +17,12 @@ import { Text } from '@tiptap/extension-text';
 import { Underline } from '@tiptap/extension-underline';
 import { Dropcursor, Placeholder, UndoRedo } from '@tiptap/extensions';
 import { type Editor, useEditor } from '@tiptap/react';
+import { marked } from 'marked';
 import { type DependencyList, useMemo } from 'react';
 import { isDefined } from 'twenty-shared/utils';
 
+export type AdvancedTextEditorContentType = 'json' | 'markdown';
+
 type UseAdvancedTextEditorProps = {
   placeholder: string | undefined;
   readonly: boolean | undefined;
@@ -30,6 +33,7 @@ type UseAdvancedTextEditorProps = {
   onImageUpload?: (file: File) => Promise<string>;
   onImageUploadError?: (error: Error, file: File) => void;
   enableSlashCommand?: boolean;
+  contentType?: AdvancedTextEditorContentType;
 };
 
 export const useAdvancedTextEditor = (
@@ -43,9 +47,12 @@ export const useAdvancedTextEditor = (
     onImageUpload,
     onImageUploadError,
     enableSlashCommand,
+    contentType = 'json',
   }: UseAdvancedTextEditorProps,
   dependencies?: DependencyList,
 ) => {
+  const isMarkdownMode = contentType === 'markdown';
+
   const extensions = useMemo(
     () => [
       Document,
@@ -87,12 +94,23 @@ export const useAdvancedTextEditor = (
     ],
   );
 
+  const getEditorContent = () => {
+    if (!isDefined(defaultValue)) {
+      return undefined;
+    }
+
+    if (isMarkdownMode) {
+      // Convert markdown to HTML, then TipTap will parse the HTML
+      return marked.parse(defaultValue, { async: false }) as string;
+    }
+
+    return getInitialAdvancedTextEditorContent(defaultValue);
+  };
+
   const editor = useEditor(
     {
       extensions,
-      content: isDefined(defaultValue)
-        ? getInitialAdvancedTextEditorContent(defaultValue)
-        : undefined,
+      content: getEditorContent(),
       editable: !readonly,
       onUpdate: ({ editor }) => {
         onUpdate(editor);