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superseded docs under docs/.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/03-data-model.md

@@ -15,7 +15,6 @@ erDiagram
     content ||--o{ player_edit : "edited (cascade)"
     content ||--o{ player_feedback : "playing"
     playlist ||--o{ content : "playlist_content M2M (position,duration,muted,edit_on_player_enabled)"
-    content }o--o{ group : "group_content M2M (legacy)"
     player_user ||--o{ player_edit : "user_code"
     https_config ||--o| https_config : "singleton row"
 ```
@@ -74,8 +73,8 @@ Methods: `is_online` (5-min window), `update_status()`, `set_password()/check_pa
 | `description` | Text | nullable |
 | `uploaded_at` | DateTime | NOT NULL, indexed |
 
-Relationships: `playlists` (M2M via `playlist_content`), `groups` (M2M via `group_content`).  
-Properties/methods: `file_size_mb`, `group_count`, `original_display_name`, `original_media_path`, `current_media_path`, `is_image()/is_video()/is_pdf()/is_weblink()`, `has_player_edits`.
+Relationships: `playlists` (M2M via `playlist_content`).  
+Properties/methods: `file_size_mb`, `original_display_name`, `original_media_path`, `current_media_path`, `is_image()/is_video()/is_pdf()/is_weblink()`, `has_player_edits`.
 
 ### `playlist` — ordered collections of content
 | Column | Type | Notes |
@@ -168,15 +167,13 @@ Classmethods: `log_info`, `log_warning`, `log_error`.
 
 Classmethods: `get_config()` (first row), `create_or_update(...)`. Method: `to_dict()`.
 
-### `group` + `group_content` — **ARCHIVED / LEGACY**
-| Column | Type | Notes |
-|---|---|---|
-| `id` | Integer | PK |
-| `name` | String(100) | unique, NOT NULL, indexed |
-| `description` | Text | nullable |
-| `created_at` / `updated_at` | DateTime | NOT NULL |
+### `group` + `group_content` — **REMOVED**
 
-`group_content(group_id, content_id)` composite-PK M2M. The current `Player` model has **no** `group_id` column — group features are archived (see [09 · Legacy](09-legacy-and-migrations.md)).
+The `Group` model, the `group_content` association table, `Content.groups` /
+`Content.group_count`, and the group-management utility functions were **deleted**
+during the code sanitization pass (the feature was archived and the table had no
+rows). `Player` never had a `group_id` column. See
+[SANITIZATION-REVIEW.md](SANITIZATION-REVIEW.md).
 
 ---
 
@@ -185,7 +182,6 @@ Classmethods: `get_config()` (first row), `create_or_update(...)`. Method: `to_d
 | Relationship | Cardinality | FK / Mechanism |
 |---|---|---|
 | `playlist` → `content` | M:N | `playlist_content` (positioned, with extras) |
-| `group` → `content` | M:N | `group_content` (legacy) |
 | `player` → `playlist` | N:1 | `player.playlist_id` (ON DELETE SET NULL) |
 | `player` → `player_feedback` | 1:N | `player_feedback.player_id` (cascade) |
 | `player` → `player_edit` | 1:N | `player_edit.player_id` (cascade) |