feat: mobile UI, chat history search, news source filtering

- Mobile (#11): responsive 3-button bottom nav (STATS/CHAT/INFO), panel switching, compact topbar, touch-friendly inputs; panels show one-at-a-time on screens <900px
- Search (#12): 🔍 button next to TRANSMIT opens search modal; history.php endpoint queries conversations table; results show role, timestamp, and snippet
- News filter (#13): ⚙ gear on NEWS tab reveals category checkboxes; hidden categories stored in localStorage; empty-state message when all hidden

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/endpoints/history.php

@@ -0,0 +1,21 @@
+<?php
+// Chat history search endpoint
+require_once __DIR__ . '/../config.php';
+require_once __DIR__ . '/../../includes/auth.php';
+
+header('Content-Type: application/json');
+AuthMiddleware::requireAuth();
+
+$q = trim($_GET['q'] ?? '');
+if (strlen($q) < 2) {
+    echo json_encode(['results' => [], 'error' => 'Query too short']);
+    exit;
+}
+
+$rows = JarvisDB::query(
+    "SELECT role, content, created_at FROM conversations
+     WHERE content LIKE ? ORDER BY created_at DESC LIMIT 25",
+    ['%' . $q . '%']
+) ?? [];
+
+echo json_encode(['results' => $rows, 'total' => count($rows)]);