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/components/backbtn.js

@@ -0,0 +1,11 @@
+// Blackflame-themed back button for detail/reading views. Goes back in history
+// (hash navigation is in history); falls back to home if there's nowhere to go.
+import { el } from '../dom.js';
+
+export function backButton() {
+  return el('button', {
+    class: 'ghost back-btn',
+    title: 'Back',
+    onclick: () => { if (history.length > 1) history.back(); else location.hash = '#/'; }
+  }, '← Back');
+}

public/components/markdown_editor.js

@@ -51,6 +51,7 @@ export function markdownEditor({ initial = '', save }) {
   }, 'Save');
 
   const toggle = el('button', {
+    class: 'ghost',
     onclick: () => {
       editing = !editing;
       if (editing) {