Sanitize codebase, reorganize docs, and add missing deploy files

Remove dead code identified in docs/SANITIZATION-REVIEW.md:
- app/blueprints/content_old.py and app/blueprints/playlist.py
- app/models/group.py, app/utils/nginx_config_reader.py
- orphaned templates (content_list, edit_content, upload_content,
  player_page) and the related group/Template references

Result: 6 blueprints, 82 routes, no dead modules or orphan templates.

Add files that deploy.sh and docker-entrypoint.sh already require but
which were never tracked:
- https_manager.py       (referenced by deploy.sh, migrate_network.sh,
                          docker-entrypoint.sh)
- Caddyfile.example      (seeded by deploy.sh; its absence aborts deploy)

Relocate generated Graphify artifacts from graphify-out/ to
docs/graphify-out/ (110 files, no content change) and archive the
superseded docs under docs/.

Ignore hygiene:
- ignore ad-hoc .env backups (.env.bak*) — they contain live secrets
- keep the pre-sanitization snapshots (docs/legacy code/,
  docs/old_code_documentation/) on disk but out of the repo

Fix .env.example: drop a duplicated config block, genericize the
hardcoded host IP, and document HOSTNAME_INTERNAL.

docs/04-application-core.md

@@ -40,7 +40,9 @@ def register_blueprints(app):
     ...
 ```
 
-> Note: `app.blueprints.content_old` is **not** imported — it is dead/legacy code.
+> Note: `content_old.py` (legacy content routes) was **deleted** during the code
+> sanitization pass — see [SANITIZATION-REVIEW.md](SANITIZATION-REVIEW.md). The
+> legacy `playlist.py` blueprint remains (redirect-only).
 
 ---
 
@@ -153,9 +155,8 @@ app/templates/
 ├── admin/           admin.html, user_management.html, leftover_media.html,
 │                    dependencies.html, customize_logos.html, editing_users.html,
 │                    https_config.html, build_player.html
-├── content/         content_list.html (legacy), content_list_new.html (modern),
-│                    media_library.html, upload_content.html (legacy),
-│                    upload_media.html, manage_playlist_content.html, edit_content.html
+├── content/         content_list_new.html, media_library.html,
+│                    upload_media.html, manage_playlist_content.html
 ├── players/         players_list.html, add_player.html, edit_player.html,
 │                    manage_player.html, player_page.html, player_fullscreen.html,
 │                    edited_media.html, edited_media_report.html, _deploy_badge.html