fix(sync-php): read Authorization via getallheaders and tolerate ETag forms

Apache commonly strips Authorization before PHP sees it, so every request looked unauthenticated on a stock XAMPP and answered 404.

If-None-Match is now compared on the bare hash: a validator that lost its quotes, or a weak W/ tag, would never match and each request would silently re-download the whole snapshot - expensive on mobile data and invisible in the logs, a 200 looking perfectly normal.

server-php/sync.php

@@ -41,10 +41,22 @@ header('X-Content-Type-Options: nosniff');
 // Authentication
 // ---------------------------------------------------------------------------
 
-/** Bearer token, compared in constant time so a wrong guess leaks no timing. */
+/**
+ * Bearer token, compared in constant time so a wrong guess leaks no timing.
+ *
+ * Three sources on purpose: Apache commonly strips Authorization before PHP
+ * sees it (it is only forwarded with CGIPassAuth on, or through a rewrite), so
+ * $_SERVER alone answers empty on a stock XAMPP and every request looks
+ * unauthenticated. getallheaders() reads what the client actually sent.
+ */
 function client_token(): string {
     $h = $_SERVER['HTTP_AUTHORIZATION'] ?? $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] ?? '';
-    if (stripos($h, 'Bearer ') === 0) return substr($h, 7);
+    if ($h === '' && function_exists('getallheaders')) {
+        foreach (getallheaders() as $name => $value) {
+            if (strcasecmp($name, 'Authorization') === 0) { $h = $value; break; }
+        }
+    }
+    if (stripos($h, 'Bearer ') === 0) return trim(substr($h, 7));
     return '';
 }
 
@@ -85,7 +97,12 @@ if ($method === 'HEAD' || $method === 'GET') {
     header('Last-Modified: ' . gmdate('D, d M Y H:i:s', (int)filemtime(SYNC_FILE)) . ' GMT');
 
     // Save the round trip when the client already holds this version.
-    if (trim($_SERVER['HTTP_IF_NONE_MATCH'] ?? '') === $etag) {
+    // Compared on the bare hash: a validator that loses its quotes or arrives
+    // as a weak tag (W/"…") would otherwise never match, and every request
+    // would silently download the whole snapshot again — costly on mobile data
+    // and invisible in the logs, since a 200 looks perfectly normal.
+    $sent = trim($_SERVER['HTTP_IF_NONE_MATCH'] ?? '');
+    if ($sent !== '' && trim($sent, 'W/" ') === trim($etag, '" ')) {
         http_response_code(304);
         exit;
     }