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superseded docs under docs/.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/02-knowledge-graph.md

@@ -84,7 +84,7 @@ These are the most-connected nodes (graph centrality). They are the architectura
 
 Graphify groups related code into communities. See [01-architecture.md §3](01-architecture.md#3-component-map-files--communities) for the full mapping. The largest:
 
-- **C0 · Auth & logging** (90 nodes) — login/logout/register + audit logging + legacy groups
+- **C0 · Auth & logging** (90 nodes) — login/logout/register + audit logging
 - **C1 · Admin & HTTPS** (80 nodes) — admin panel, Caddy generation, editing users
 - **C2 · Playlists & content** (68 nodes) — the modern content/playlist workflow
 - **C3 · Player API & edits** (62 nodes) — player-facing REST + edited-media pipeline