feat: add weblink playlists, SSH player deployment, Caddy HTTPS, build player page

- Content model: add url column + is_weblink() for web page content items
- Player model: add deployment tracking fields (status, timestamps, message)
- Content blueprint: add add_weblink and add_weblink_to_playlist routes;
  weblinks auto-deleted when removed from playlist
- Players blueprint: add SSH deploy mode in add_player; weblink-aware playlist
- API blueprint: weblink URL served directly in playlist response;
  add /api/deploy/test-ssh and /api/deploy/player endpoints
- Admin blueprint: add build-player page (clone from Gitea, write base config);
  replace nginx status card with Caddy status on HTTPS config page
- caddy_manager: rewritten to generate proper HTTPS/internal-CA Caddyfiles
  and reload Caddy via admin API (/load) for live config updates
- ssh_deploy, background_tasks, player_build: new utils for SSH deployment
- background_tasks: push Flask app context into background thread so DB
  updates after deployment complete correctly
- ssh_deploy: robust install script detection with passwordless sudo injection
  (uses SSH credentials, cleaned up after install)
- Dockerfile: add git, sshpass, openssh-client, rsync
- docker-compose: switch nginx to Caddy on ports 80/443; add port 5000 for dev
- Templates: add_player deploy mode UI, weblink form in playlist/upload pages,
  build_player admin page, Caddy status on HTTPS config page
- Migrations: add_url_to_content, add_deployment_fields_to_player
- app.py: call db.create_all() on startup for schema bootstrap
- config.py: add PLAYER_CODE_DIR and PLAYER_REPO_URL settings

app/models/content.py

@@ -24,6 +24,9 @@ class Content(db.Model):
     content_type = db.Column(db.String(50), nullable=False, index=True)
     duration = db.Column(db.Integer, default=10, nullable=True)
     file_size = db.Column(db.BigInteger, nullable=True)
+    # For 'weblink' content this holds the web page URL to display on the player.
+    # NULL for file-based content (image/video/pdf).
+    url = db.Column(db.String(2048), nullable=True)
     description = db.Column(db.Text, nullable=True)
     uploaded_at = db.Column(db.DateTime, default=datetime.utcnow, 
                            nullable=False, index=True)
@@ -61,3 +64,7 @@ class Content(db.Model):
     def is_pdf(self) -> bool:
         """Check if content is a PDF."""
         return self.content_type == 'pdf'
+    
+    def is_weblink(self) -> bool:
+        """Check if content is a web link (URL) rather than an uploaded file."""
+        return self.content_type == 'weblink'