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superseded docs under docs/.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/05-blueprints-api.md

@@ -1,6 +1,6 @@
 # 05 · Blueprints & REST API
 
-DigiServer v2 registers **7 active blueprints** (`content_old.py` is legacy dead code and is not registered).
+DigiServer v2 registers **7 active blueprints**.
 
 ---
 
@@ -203,7 +203,7 @@ Redirects/legacy — kept for compatibility:
 |---|---|---|---|
 | `/player-feedback` | POST | `receive_player_feedback` | Status (playing/paused/error/restarting); infers player; **auto-marks deployment `deployed`** |
 | `/player-status/<player_id>` | GET | `get_player_status` | Online (5-min), latest feedback |
-| `/system-info` | GET | — | Counts: players online/total, groups, content, 24h logs |
+| `/system-info` | GET | — | Counts: players online/total, content, 24h logs |
 | `/content` | GET | — | List content with counts |
 | `/logs` | GET | `get_logs` | Query logs (`limit`/`level`/`since`) |