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superseded docs under docs/.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.

app/utils/__init__.py

@@ -10,14 +10,7 @@ from app.utils.uploads import (
     get_file_size,
     delete_file
 )
-from app.utils.group_player_management import (
-    get_player_status_info,
-    get_group_statistics,
-    assign_player_to_group,
-    bulk_assign_players_to_group,
-    get_online_players_count,
-    get_players_by_status
-)
+from app.utils.group_player_management import get_player_status_info
 from app.utils.pptx_converter import pptx_to_pdf_libreoffice, validate_pptx_file
 
 __all__ = [
@@ -36,13 +29,8 @@ __all__ = [
     'clear_upload_progress',
     'get_file_size',
     'delete_file',
-    # Group/Player Management
+    # Player Management
     'get_player_status_info',
-    'get_group_statistics',
-    'assign_player_to_group',
-    'bulk_assign_players_to_group',
-    'get_online_players_count',
-    'get_players_by_status',
     # PPTX Converter
     'pptx_to_pdf_libreoffice',
     'validate_pptx_file',