feat: implement nib design system — warm amber palette, dual themes, new typography

Replace Tokyonight/Catppuccin blue palette with warm amber/ink identity.
Dual theme support (noir + paper) via data-theme attribute with
localStorage persistence. Space Grotesk for chrome, Monaspace Neon for
content. Updated glyph set (Strokes: — ○ ◇) across web and CLI.

web/app.js

@@ -2,7 +2,7 @@
   'use strict';
 
   const GLYPHS = {
-    note: '◦', todo: '▸', event: '◇',
+    note: '—', todo: '○', event: '◇',
     snippet: '◆', template: '◈', checklist: '☐',
     decision: '⚖', link: '↗',
   };
@@ -222,7 +222,7 @@
       const groups = groupByDate(state.entities);
       let idx = 0;
       for (const g of groups) {
-        html += `<div class="date-header">── ${g.label} ──</div>`;
+        html += `<div class="date-header">${g.label}</div>`;
         for (const e of g.entities) {
           html += renderEntityItem(e, idx);
           idx++;
@@ -754,6 +754,20 @@
     return escHtml(s).replace(/'/g, '&#39;');
   }
 
+  // ========== Theme ==========
+
+  const themeToggle = $('#theme-toggle');
+  let nibTheme = localStorage.getItem('nib:theme') || 'dark';
+  document.documentElement.setAttribute('data-theme', nibTheme);
+  themeToggle.textContent = nibTheme === 'paper' ? '◐' : '◑';
+
+  themeToggle.addEventListener('click', () => {
+    nibTheme = nibTheme === 'dark' ? 'paper' : 'dark';
+    document.documentElement.setAttribute('data-theme', nibTheme);
+    localStorage.setItem('nib:theme', nibTheme);
+    themeToggle.textContent = nibTheme === 'paper' ? '◐' : '◑';
+  });
+
   // ========== Init ==========
 
   async function init() {