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/blueprints/main.py

@@ -89,6 +89,50 @@ def dashboard():
     )
 
 
+@main_bp.route('/help')
+@login_required
+def help_page():
+    """User manual / help page.
+
+    The manual lives at ``app/static/help/_manual_body.html`` — a pre-rendered
+    HTML fragment generated from ``documentatie/Manual-Utilizare-DigiServer.md``
+    with ``pandoc`` (see ``documentatie/convert_help_page.sh``).
+
+    It is shipped as a static asset rather than parsed at runtime on purpose:
+    it keeps the runtime free of a Markdown dependency and means the help page
+    renders identically regardless of what is installed in the container.
+    """
+    import os
+    import re
+
+    base_dir = os.path.dirname(os.path.dirname(__file__))  # -> app/
+    manual_path = os.path.join(base_dir, 'static', 'help', '_manual_body.html')
+
+    manual_html = ''
+    toc = []
+    try:
+        with open(manual_path, 'r', encoding='utf-8') as f:
+            manual_html = f.read()
+
+        # Build the sidebar from the level-2 headings (`<h2 id="...">`), which
+        # is exactly the printed table of contents of the manual. Nested <h3>
+        # entries would make the sidebar unwieldy, so they are left out.
+        for anchor, title in re.findall(
+            r'<h2 id="([^"]+)"[^>]*>(.*?)</h2>', manual_html, re.DOTALL
+        ):
+            clean = re.sub(r'<[^>]+>', '', title).strip()
+            if clean:
+                toc.append({'anchor': anchor, 'title': clean})
+    except FileNotFoundError:
+        manual_html = (
+            '<h1>Manual indisponibil</h1>'
+            '<p>Fișierul manualului nu a fost găsit. '
+            'Rulați <code>documentatie/convert_help_page.sh</code> pentru a-l genera.</p>'
+        )
+
+    return render_template('help.html', manual_html=manual_html, toc=toc)
+
+
 @main_bp.route('/health')
 def health():
     """Health check endpoint"""