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/project.js

@@ -1,6 +1,7 @@
 // Project view — header + tasks (with inline status toggle) + pages + refs + add-task form.
 import { api } from '../api.js';
 import { el, mount, clear } from '../dom.js';
+import { backButton } from '../components/backbtn.js';
 
 const STATUSES = ['todo', 'doing', 'blocked', 'done'];
 const STATUS_CLASS = { todo: 'idle', doing: 'warn', blocked: 'bad', done: 'ok' };
@@ -75,6 +76,7 @@ export async function render(main, ctx) {
   newTitle.addEventListener('keydown', (e) => { if (e.key === 'Enter') addTask(); });
 
   mount(main,
+    backButton(),
     el('h1', { class: 'view-h1' }, proj.name),
     el('p', { class: 'view-sub' },
       el('span', { class: 'status ' + (proj.status === 'done' ? 'ok' : proj.status === 'paused' ? 'warn' : '') }, proj.status),