fix tfe page: scope common.css header to body>header, fix grid width collapse, remove overflow-y clip

TODO.md

@@ -1,6 +1,10 @@
 # TODO
 
 ## Done
+- [x] Fix TFE page gradient bleed & layout collapse
+  - [x] Scope `header` nav CSS in common.css to `body > header` (prevents article `<header>` inheriting gradient)
+  - [x] Add `width: 100%` + `align-items: start` to `.tfe-layout` grid
+  - [x] Remove `overflow-y: auto` from `.tfe-main` (was clipping layout)
 - [x] Redesign TFE detail page
   - [x] Author moved above title (smaller body font)
   - [x] Remove "← Retour" back link