Add Oasis-Mobile-UX theme with hexagon navigation

- Selectable Oasis-Mobile-UX theme; mobile.css kept intact
- Hexagon category launcher on home (10 categories with expandable modules)
- Customizable bottom bar (up to 4 shortcuts, Peers/Invites fixed)
- Empty states and collapsible activity filters

src/backend/backend.js

@@ -7887,6 +7887,28 @@ router
     saveConfig(cfg);
     ctx.redirect(`/modules`);
   })
+  .get("/settings/bottombar", async (ctx) => {
+    ctx.body = require("../views/main_views").bottomBarPickerView();
+  })
+  .post("/settings/bottombar", koaBody(), async (ctx) => {
+    const cfg = getConfig();
+    const MAX = 4;
+    const body = ctx.request.body || {};
+    const action = String(body.action || '').trim();
+    const key = String(body.key || '').trim();
+    const catalog = require("../views/main_views").PINNABLE_MODULES || [];
+    let pins = Array.isArray(cfg.bottomBarPins) ? cfg.bottomBarPins.slice() : [];
+    if (action === 'add') {
+      if (key && catalog.some(m => m.key === key) && !pins.includes(key) && pins.length < MAX) pins.push(key);
+    } else if (action === 'remove') {
+      pins = pins.filter(k => k !== key);
+    } else if (action === 'clear') {
+      pins = [];
+    }
+    cfg.bottomBarPins = pins.slice(0, MAX);
+    saveConfig(cfg);
+    ctx.redirect('/settings/bottombar');
+  })
   .post("/settings/ai", koaBody(), async (ctx) => {
     const aiPrompt = String(ctx.request.body.ai_prompt || "").trim();
     if (aiPrompt.length > 128) { sendErrorPage(ctx, "Prompt too long. Must be 128 characters or fewer.", { status: 400 }); return; }