feat: server-side theme save/load via theme.json

- Server reads from theme.json (separate from config.json), hot-loads on every request
- POST /api/config/theme writes theme.json directly — no manual file editing
- GET /api/config/theme now merges: defaults → config.json → theme.json
- Also returns themeDark and typeColors (were missing from API)
- Customizer: replaced 'merge into config.json' instructions with Save/Load Server buttons
- JSON export moved to collapsible details section
- theme.json added to .gitignore (instance-specific)

.gitignore

@@ -6,3 +6,4 @@ data/
 config.json
 data-lincomatic/
 config-lincomatic.json
+theme.json

public/customize.js

@@ -597,18 +597,19 @@
         (hasUserTheme ? '<button class="cust-reset-user" id="custResetUser">🗑️ Reset my theme</button>' : '') +
       '</div>' +
       '<hr style="border:none;border-top:1px solid var(--border);margin:16px 0">' +
-      '<p class="cust-section-title">Admin Export</p>' +
-      '<p style="font-size:12px;color:var(--text-muted);margin-bottom:8px">Export as config.json for server deployment — applies to all users of this instance.</p>' +
-      '<textarea class="cust-export-area" readonly id="custExportJson">' + esc(json) + '</textarea>' +
+      '<p class="cust-section-title">Admin — Server Theme</p>' +
+      '<p style="font-size:12px;color:var(--text-muted);margin-bottom:8px">Save/load the theme on the server. Applies to all users who haven\'t set their own.</p>' +
+      '<div class="cust-export-btns" style="margin-bottom:12px">' +
+        '<button class="cust-save-user" id="custSaveServer">📡 Save to Server</button>' +
+        '<button class="cust-dl-btn" id="custLoadServer">📥 Load from Server</button>' +
+      '</div>' +
+      '<details style="margin-top:8px"><summary style="font-size:12px;font-weight:600;cursor:pointer;color:var(--text-muted)">Export as JSON</summary>' +
+      '<textarea class="cust-export-area" readonly id="custExportJson" style="margin-top:8px">' + esc(json) + '</textarea>' +
       '<div class="cust-export-btns">' +
-        '<button class="cust-copy-btn" id="custCopy">📋 Copy to Clipboard</button>' +
-        '<button class="cust-dl-btn" id="custDownload">💾 Download config-theme.json</button>' +
-      '</div>' +
-      '<div class="cust-instructions">' +
-        '<strong>How to apply:</strong><br>' +
-        'Merge this JSON into your <code>config.json</code> file and restart the server.<br>' +
-        'Only values that differ from defaults are included.' +
+        '<button class="cust-copy-btn" id="custCopy">📋 Copy</button>' +
+        '<button class="cust-dl-btn" id="custDownload">💾 Download</button>' +
       '</div>' +
+      '</details>' +
     '</div>';
   }
 
@@ -864,6 +865,43 @@
       render(container);
       applyThemePreview(); autoSave();
     });
+
+    // Save to server
+    var saveServerBtn = document.getElementById('custSaveServer');
+    if (saveServerBtn) saveServerBtn.addEventListener('click', function () {
+      var data = buildExport();
+      fetch('/api/config/theme', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify(data)
+      }).then(function (r) {
+        if (!r.ok) throw new Error('Server returned ' + r.status);
+        return r.json();
+      }).then(function () {
+        saveServerBtn.textContent = '✓ Saved to server!';
+        setTimeout(function () { saveServerBtn.textContent = '📡 Save to Server'; }, 2000);
+      }).catch(function (e) {
+        saveServerBtn.textContent = '✕ Failed: ' + e.message;
+        setTimeout(function () { saveServerBtn.textContent = '📡 Save to Server'; }, 3000);
+      });
+    });
+
+    // Load from server
+    var loadServerBtn = document.getElementById('custLoadServer');
+    if (loadServerBtn) loadServerBtn.addEventListener('click', function () {
+      fetch('/api/config/theme').then(function (r) { return r.json(); }).then(function (cfg) {
+        window.SITE_CONFIG = cfg;
+        resetPreview();
+        initState();
+        applyThemePreview();
+        render(container);
+        loadServerBtn.textContent = '✓ Loaded!';
+        setTimeout(function () { loadServerBtn.textContent = '📥 Load from Server'; }, 2000);
+      }).catch(function (e) {
+        loadServerBtn.textContent = '✕ Failed';
+        setTimeout(function () { loadServerBtn.textContent = '📥 Load from Server'; }, 3000);
+      });
+    });
   }
 
   function toggle() {

server.js

@@ -383,19 +383,32 @@ function getObserverIdsForRegions(regionParam) {
   return ids;
 }
 
+// Theme: load from separate theme.json (falls back to config.json keys for compat)
+const THEME_PATH = path.join(__dirname, 'theme.json');
+function loadThemeFile() {
+  try { return JSON.parse(fs.readFileSync(THEME_PATH, 'utf8')); } catch { return {}; }
+}
+
 app.get('/api/config/theme', (req, res) => {
+  const theme = loadThemeFile();
   res.json({
     branding: {
       siteName: 'MeshCore Analyzer',
       tagline: 'Real-time MeshCore LoRa mesh network analyzer',
-      ...(config.branding || {})
+      ...(config.branding || {}),
+      ...(theme.branding || {})
     },
     theme: {
       accent: '#4a9eff',
       accentHover: '#6db3ff',
       navBg: '#0f0f23',
       navBg2: '#1a1a2e',
-      ...(config.theme || {})
+      ...(config.theme || {}),
+      ...(theme.theme || {})
+    },
+    themeDark: {
+      ...(config.themeDark || {}),
+      ...(theme.themeDark || {})
     },
     nodeColors: {
       repeater: '#dc2626',
@@ -403,12 +416,28 @@ app.get('/api/config/theme', (req, res) => {
       room: '#16a34a',
       sensor: '#d97706',
       observer: '#8b5cf6',
-      ...(config.nodeColors || {})
+      ...(config.nodeColors || {}),
+      ...(theme.nodeColors || {})
     },
-    home: config.home || null,
+    typeColors: {
+      ...(config.typeColors || {}),
+      ...(theme.typeColors || {})
+    },
+    home: theme.home || config.home || null,
   });
 });
 
+app.post('/api/config/theme', express.json(), (req, res) => {
+  try {
+    const data = req.body;
+    if (!data || typeof data !== 'object') return res.status(400).json({ error: 'Invalid JSON' });
+    fs.writeFileSync(THEME_PATH, JSON.stringify(data, null, 2), 'utf8');
+    res.json({ ok: true });
+  } catch (e) {
+    res.status(500).json({ error: e.message });
+  }
+});
+
 app.get('/api/config/map', (req, res) => {
   const defaults = config.mapDefaults || {};
   res.json({