docs: more cleanup following restructure (#2702)

- add TOC for Reference section
- make external links use _blank to open a new tab
- fix some more /gen links spots I missed, oops
- add a general redirect from old /gen links → /reference
- some more stylistic touchups

### Change Type

- [x] `documentation` — Changes to the documentation only[^2]

### Release Notes

- Docs: further cleanup following restructure.

apps/docs/utils/ContentDatabase.ts

@@ -276,8 +276,7 @@ export class ContentDatabase {
 				// Cache the links structure for next time
 				if (sectionId === 'examples') {
 					this._sidebarExamplesContentLinks = links
-				}
-				if (sectionId === 'reference') {
+				} else if (sectionId === 'reference') {
 					this._sidebarReferenceContentLinks = links
 				} else {
 					this._sidebarContentLinks = links