feat: env-driven upload limits + request timeout, inline video playback, range requests

- Add UPLOAD_FILE_LIMIT_MB/UPLOAD_TOTAL_LIMIT_MB env (defaults 50/200), compute request timeout from total limit or UPLOAD_REQUEST_TIMEOUT_MS
- Expose upload limits via /api/public-settings and sync in frontend (remove hardcoded 50MB assumption)
- Add byte-range support in storage (getRange/streamRangeTo) and serve Content-Range/Accept-Ranges for S3/local
- Implement inline playable video delivery for browser formats (mp4/m4v/webm/ogv) with ?play=1, range requests, proper 206/416
- Add video modal in journal UI with player and download fallback
- Update docs (AGENTS.md/PRD.md/README.md), styles for video modal, add instructions/TODO.md and screenshots
- Extend MIME types for media

public/journal.html

@@ -66,6 +66,17 @@
   <img id="imgModalSrc">
 </div>
 
+<div class="modal-overlay" id="videoModal">
+  <div class="video-modal">
+    <div class="video-head">
+      <span id="videoTitle"></span>
+      <a class="video-dl" id="videoDownload" download title="Скачать файл">Скачать</a>
+      <button type="button" class="video-close" id="videoClose" title="Закрыть">&times;</button>
+    </div>
+    <video id="videoPlayer" controls playsinline preload="metadata"></video>
+  </div>
+</div>
+
 <div class="modal-overlay" id="editModal">
   <div class="edit-modal" style="max-width:720px">
     <h3>Редактирование записи</h3>