Show the name as LogStream in the interface

Titles, header, login page, help texts (FR/EN) and auth error pages.
Technical identifiers (Go module, binary, compose services, cookies,
localStorage keys, logstream.exclude label) are unchanged.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

web/index.html

@@ -3,7 +3,7 @@
 <head>
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1">
-  <title>Logstream</title>
+  <title>LogStream</title>
   <link rel="icon" href="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 32 32'%3E%3Crect width='32' height='32' rx='8' fill='%236366f1'/%3E%3Cpath d='M8 10h16M8 16h11M8 22h14' stroke='white' stroke-width='3' stroke-linecap='round'/%3E%3C/svg%3E">
   <link rel="stylesheet" href="style.css">
   <script>
@@ -20,7 +20,7 @@
   <header class="topbar">
     <div class="brand">
       <svg viewBox="0 0 32 32" aria-hidden="true"><rect width="32" height="32" rx="8"/><path d="M8 10h16M8 16h11M8 22h14"/></svg>
-      <span>Logstream</span>
+      <span>LogStream</span>
     </div>
 
     <div class="search">