feat(ui): blackflame theming pass — edit toggle, md tables, back button, Little Blue action cards

- markdown_editor Edit toggle uses themed ghost button
- .md-preview gets full blackflame styling incl. tables (migrated BookStack tables now render as tables)
- reusable back button on page/reference/project/resource reading views
- Little Blue actions regrouped into themed cards, pairing Start/Stop per guest

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/views/page.js

@@ -2,6 +2,7 @@
 import { api } from '../api.js';
 import { el, mount } from '../dom.js';
 import { markdownEditor } from '../components/markdown_editor.js';
+import { backButton } from '../components/backbtn.js';
 
 export async function render(main, ctx) {
   const id = ctx.params.id;
@@ -28,6 +29,7 @@ export async function render(main, ctx) {
   );
 
   mount(main,
+    backButton(),
     el('h1', { class: 'view-h1' }, page.title),
     el('p', { class: 'view-sub muted' }, '/' + page.slug),
     editor,