Server: faster releases (cache hashes), per-version skip, longer signed-URL TTL

- gate.php : ETag now derived from size+mtime instead of md5_file($zip).
  Previously the gate hashed the entire 14 GB ZIP on every HEAD/GET call
  (including each of 8 parallel segments) → 30s-5min preparation lag for
  clients before the first byte. Now <1ms per request.
- SignManifest : disk-backed cache for SHA-256 keyed by (path,size,mtime).
  Re-signing 5×14 GB versions used to take ~25 min, now ~1s when nothing
  changed. New "Force re-hash" toggle in admin to ignore the cache.
- versions.php : per-row "🔁 Hash" button to sign a single version, plus
  a "⚙ Hash" dropdown to toggle hashAlgorithm:none for builds where the
  user accepts skipping client-side verification (manifest stays signed
  Ed25519, only the per-ZIP SHA-256 verification is bypassed).
- DownloadUrl.php : signed-URL TTL bumped 1h → 6h to cover slow ADSL users
  who need >1h to finish a 14 GB download.
- .gitignore : track server/builds/.htaccess + gate.php (still ignore the
  actual ZIP/exe binaries).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/admin/launcher.php

@@ -70,8 +70,10 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
         elseif ($action === 'sync_launcher') {
             require_once "$root/tools/SignManifest.php";
             $signer = new \PSLauncher\Tools\SignManifest($root);
-            $result = $signer->run('launcher');
-            $message = "Sortie du script (scope: launcher) :\n" . implode("\n", $result['log']);
+            $force = !empty($_POST['force']);
+            $result = $signer->run('launcher', $force);
+            $forceLabel = $force ? ' [FORCE: cache ignoré]' : '';
+            $message = "Sortie du script (scope: launcher{$forceLabel}) :\n" . implode("\n", $result['log']);
             if (!$result['ok']) $messageType = 'error';
         }
     } catch (Exception $e) {
@@ -159,6 +161,9 @@ Layout::header('Launcher', 'launcher');
         <?= Layout::csrfField() ?>
         <input type="hidden" name="action" value="sync_launcher">
         <button class="btn btn-primary" type="submit">🔁 Hasher le launcher + signer</button>
+        <label style="margin-left:12px;font-size:12px;color:#888" title="Recalcule le SHA-256 même si l'exe n'a pas changé.">
+            <input type="checkbox" name="force" value="1"> Force re-hash
+        </label>
     </form>
 
     <?php if ($launcher): ?>