Add in-app help page with user manual (Romanian)

Adds a /help page served from the dashboard navigation, containing the full
Romanian user manual for operators: dashboard, playlist management, adding
media, removing files from playlists, player management, and the advanced
edited-media view.

Implementation notes
- Manual is pre-rendered to HTML with pandoc and shipped as a static asset
  (app/static/help/_manual_body.html) rather than parsed at runtime. This
  keeps the container free of a Markdown dependency and makes the page render
  identically regardless of what is installed.
- /help is login-protected; the sidebar table of contents is derived from the
  level-2 headings at request time.
- Screenshots are served from app/static/help/screenshots/ (32 images).
- Regenerate after editing the manual:
    documentatie/convert_help_page.sh
    docker compose up -d --build

Also adds
- backup_players_playlists.sh / restore_database.sh for DB backup and restore.
- .gitignore rules so local database backups (real production data), generated
  .docx files and duplicate screenshot copies are never committed.

app/static/icons/help.svg

@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+  <circle cx="12" cy="12" r="10"></circle>
+  <path d="M9.09 9a3 3 0 0 1 5.83 1c0 2-3 3-3 3"></path>
+  <line x1="12" y1="17" x2="12.01" y2="17"></line>
+</svg>