feat: fix junction toggle persistence and add type-safe documentation paths (#17421)

## Summary

- **Fix junction relation toggle not being saved**: The form schema
wasn't tracking the `settings` field, so changes to
`junctionTargetFieldId` weren't marked as dirty
- **Add type-safe documentation paths**: Generate TypeScript constants
from `base-structure.json` to prevent broken documentation links
- **Create many-to-many relations documentation**: Step-by-step guide
for building many-to-many relations using junction objects
- **Update `getDocumentationUrl`**: Now uses shared constants from
`twenty-shared` for base URL, default path, and supported languages

## Key Changes

### Junction Toggle Fix
- Added `settings` field to the form schema in
`SettingsDataModelFieldRelationForm.tsx`
- Fixed the toggle to properly merge settings when updating
`junctionTargetFieldId`

### Type-Safe Documentation Paths
- New constants in `twenty-shared/constants`:
- `DOCUMENTATION_PATHS` - All 161 documentation paths as typed constants
  - `DOCUMENTATION_SUPPORTED_LANGUAGES` - 14 supported languages
  - `DOCUMENTATION_BASE_URL` / `DOCUMENTATION_DEFAULT_PATH`
- Generator script: `yarn docs:generate-paths`
- CI integration: Added to `docs-i18n-pull.yaml` workflow

### Documentation
- New article:
`/user-guide/data-model/how-tos/create-many-to-many-relations`
- Updated `/user-guide/data-model/capabilities/relation-fields.mdx` with
Lab warning and link

## Test plan
- [ ] Verify junction toggle saves correctly when enabled/disabled
- [ ] Verify documentation link opens correct localized page
- [ ] Verify `yarn docs:generate-paths` regenerates paths correctly

packages/twenty-docs/scripts/generate-documentation-paths.ts

@@ -0,0 +1,101 @@
+import fs from 'fs';
+import path from 'path';
+
+type BasePage = string | BaseGroup;
+
+type BaseGroup = {
+  key: string;
+  label: string;
+  icon?: string;
+  pages: BasePage[];
+};
+
+type BaseTab = {
+  key: string;
+  label: string;
+  groups: BaseGroup[];
+};
+
+type BaseStructure = {
+  tabs: BaseTab[];
+};
+
+const baseStructurePath = path.resolve(
+  __dirname,
+  '../navigation/base-structure.json',
+);
+
+const outputDir = path.resolve(__dirname, '../../twenty-shared/src/constants');
+
+const baseStructure: BaseStructure = JSON.parse(
+  fs.readFileSync(baseStructurePath, 'utf8'),
+);
+
+const extractPaths = (pages: BasePage[]): string[] => {
+  const paths: string[] = [];
+
+  for (const page of pages) {
+    if (typeof page === 'string') {
+      paths.push(page);
+    } else {
+      paths.push(...extractPaths(page.pages));
+    }
+  }
+
+  return paths;
+};
+
+const pathToConstantName = (docPath: string): string => {
+  return docPath.replace(/^\//, '').replace(/[/-]/g, '_').toUpperCase();
+};
+
+const allPaths: string[] = [];
+
+for (const tab of baseStructure.tabs) {
+  for (const group of tab.groups) {
+    allPaths.push(...extractPaths(group.pages));
+  }
+}
+
+const sortedPaths = [...allPaths].sort();
+
+const AUTO_GENERATED_HEADER = `/*
+ * _____                    _
+ *|_   _|_      _____ _ __ | |_ _   _
+ *  | | \\ \\ /\\ / / _ \\ '_ \\| __| | | | Auto-generated file
+ *  | |  \\ V  V /  __/ | | | |_| |_| | DO NOT EDIT - changes will be overwritten
+ *  |_|   \\_/\\_/ \\___|_| |_|\\__|\\__, | Generated by: yarn docs:generate-paths
+ *                              |___/
+ *
+ * This file is generated from packages/twenty-docs/navigation/base-structure.json
+ * To add new documentation pages, add them to base-structure.json and run:
+ *   yarn docs:generate-paths
+ */
+
+`;
+
+// Generate DocumentationPaths.ts
+const pathEntries = sortedPaths
+  .map((docPath) => {
+    const constName = pathToConstantName(docPath);
+    const value = `'/${docPath}'`;
+    // Check if line would be too long (80 char limit)
+    if (`  ${constName}: ${value},`.length > 80) {
+      return `  ${constName}:\n    ${value},`;
+    }
+    return `  ${constName}: ${value},`;
+  })
+  .join('\n');
+
+const pathsContent = `${AUTO_GENERATED_HEADER}export const DOCUMENTATION_PATHS = {
+${pathEntries}
+} as const;
+
+export type DocumentationPath =
+  (typeof DOCUMENTATION_PATHS)[keyof typeof DOCUMENTATION_PATHS];
+`;
+
+fs.writeFileSync(path.join(outputDir, 'DocumentationPaths.ts'), pathsContent);
+
+console.log(`Generated documentation constants to ${outputDir}`);
+console.log(`Total paths: ${sortedPaths.length}`);