Add SQLite-backed announcement system and admin portal

- Add SQLite database initialization and management in inc/db.php
- Implement session authentication and CSRF security helpers in inc/auth.php
- Implement announcement querying and saving in inc/announcements.php
- Add management dashboard, login, and logout in admin/
- Protect db/ directory with Apache access controls

inc/announcements.php

@@ -0,0 +1,80 @@
+<?php
+/**
+ * Announcements helper functions
+ */
+
+require_once __DIR__ . '/db.php';
+
+function get_active_announcement(): ?array {
+    $pdo = get_db();
+    $today = date('Y-m-d');
+
+    $sql = "
+        SELECT * FROM announcements 
+        WHERE is_active = 1
+          AND (start_date IS NULL OR start_date = '' OR start_date <= :today1)
+          AND (end_date IS NULL OR end_date = '' OR end_date >= :today2)
+        ORDER BY id DESC
+        LIMIT 1
+    ";
+
+    $stmt = $pdo->prepare($sql);
+    $stmt->execute([
+        ':today1' => $today,
+        ':today2' => $today
+    ]);
+    $result = $stmt->fetch();
+
+    return $result ?: null;
+}
+
+function get_all_announcements(): array {
+    $pdo = get_db();
+    $stmt = $pdo->query("SELECT * FROM announcements ORDER BY id DESC");
+    return $stmt->fetchAll();
+}
+
+function save_announcement(array $data, ?int $id = null): int {
+    $pdo = get_db();
+
+    $isActive = !empty($data['is_active']) ? 1 : 0;
+    $type = in_array($data['type'] ?? '', ['holiday', 'special', 'closure']) ? $data['type'] : 'holiday';
+    $headline = trim($data['headline'] ?? '');
+    $message = trim($data['message'] ?? '');
+    $startDate = !empty($data['start_date']) ? trim($data['start_date']) : null;
+    $endDate = !empty($data['end_date']) ? trim($data['end_date']) : null;
+    $showBanner = !empty($data['show_banner']) ? 1 : 0;
+    $showInHours = !empty($data['show_in_hours']) ? 1 : 0;
+
+    if ($id) {
+        $stmt = $pdo->prepare("
+            UPDATE announcements SET
+                is_active = ?,
+                type = ?,
+                headline = ?,
+                message = ?,
+                start_date = ?,
+                end_date = ?,
+                show_banner = ?,
+                show_in_hours = ?,
+                updated_at = CURRENT_TIMESTAMP
+            WHERE id = ?
+        ");
+        $stmt->execute([
+            $isActive, $type, $headline, $message, $startDate, $endDate,
+            $showBanner, $showInHours, $id
+        ]);
+        return $id;
+    } else {
+        $stmt = $pdo->prepare("
+            INSERT INTO announcements (
+                is_active, type, headline, message, start_date, end_date, show_banner, show_in_hours
+            ) VALUES (?, ?, ?, ?, ?, ?, ?, ?)
+        ");
+        $stmt->execute([
+            $isActive, $type, $headline, $message, $startDate, $endDate,
+            $showBanner, $showInHours
+        ]);
+        return (int)$pdo->lastInsertId();
+    }
+}