Fase 3 priority 2: presets, random style, qr scanner, PWA

Preset system: qr_presets table (migration 005) plus a presets.php AJAX
endpoint (list/save/delete, CSRF-protected, scoped to the logged-in user's
own id - presets are personal, never shared across accounts). UI/JS lives in
dist/js/qrcode-style-tools.js.

Random style button: client-side only, fills foreground/background with a
random hex color pair (playful randomize, no contrast/scannability
guarantee).

Qr scanner (scan_qrcode.php): camera or image upload, decoded entirely
client-side via html5-qrcode (CDN, pinned to 2.3.8).

PWA: manifest.json + service-worker.js, icons generated from the existing
DynamicQRCode_Original.png glyph. The service worker only caches static
assets (css/js/images) and deliberately never touches PHP pages, since those
carry CSRF tokens and session-specific content that must never be cached.

Fixes a gap found while testing: qrcode_options.php is only a shared partial
for the static qr forms - the dynamic qr form (form_dynamic_add.php) has its
own separate copy of the foreground/background/level/size/filename/format
fields (pre-existing structure, not something introduced here). That meant
frame_text and the new preset/random-style UI never showed up on the
dynamic qr page. Added the same fields there too, verified with a dynamic qr
plus frame text (150x180px, the expected +30px padding).

db/init.sql

@@ -89,6 +89,20 @@ CREATE TABLE IF NOT EXISTS `audit_log` (
   KEY `user_id` (`user_id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
+-- Fase 3 (priority 2): saved color/style presets per user
+CREATE TABLE IF NOT EXISTS `qr_presets` (
+  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
+  `user_id` int(25) NOT NULL,
+  `name` varchar(50) NOT NULL,
+  `foreground` varchar(10) NOT NULL,
+  `background` varchar(10) NOT NULL,
+  `level` varchar(1) NOT NULL DEFAULT 'L',
+  `size` int(10) unsigned NOT NULL DEFAULT 200,
+  `created_at` datetime NOT NULL,
+  PRIMARY KEY (`id`),
+  KEY `user_id` (`user_id`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8;
+
 /*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
 /*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
 /*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;