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

.github/workflows/docs-i18n-pull.yaml

@@ -107,10 +107,13 @@ jobs:
       - name: Regenerate docs.json
         run: yarn docs:generate
 
+      - name: Regenerate documentation paths constants
+        run: yarn docs:generate-paths
+
       - name: Commit artifacts to pull request branch
         if: github.event_name == 'pull_request'
         run: |
-          git add packages/twenty-docs/docs.json packages/twenty-docs/navigation/navigation.template.json
+          git add packages/twenty-docs/docs.json packages/twenty-docs/navigation/navigation.template.json packages/twenty-shared/src/constants/DocumentationPaths.ts
           if git diff --staged --quiet --exit-code; then
             echo "No navigation/doc changes to commit."
             exit 0