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superseded docs under docs/.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/tools/sanitize_templates.py

@@ -0,0 +1,65 @@
+"""Detect orphan templates (never rendered) and orphan static assets."""
+from __future__ import annotations
+
+import os
+import re
+
+# Walk up until we find the project root (robust to the tool living in a
+# nested folder such as docs/tools/).
+_here = os.path.dirname(os.path.abspath(__file__))
+while _here != os.path.dirname(_here) and not os.path.isdir(os.path.join(_here, 'app')):
+    _here = os.path.dirname(_here)
+REPO = _here
+APP = os.path.join(REPO, 'app')
+TPL = os.path.join(APP, 'templates')
+
+
+def read(p):
+    return open(p, encoding='utf-8', errors='replace').read()
+
+
+# gather all render_template('x.html') calls
+rendered = set()
+for root, dirs, files in os.walk(APP):
+    dirs[:] = [d for d in dirs if d not in ('__pycache__', 'templates')]
+    for f in files:
+        if f.endswith('.py'):
+            s = read(os.path.join(root, f))
+            rendered |= set(re.findall(r"render_template\(\s*['\"]([^'\"]+)['\"]", s))
+            # render_template with variable name - note it
+            rendered |= set(re.findall(r"render_template\(\s*([a-z_]+)", s)) - {'f'}
+
+# gather extends/include/import references
+refs = set()
+for root, dirs, files in os.walk(TPL):
+    for f in files:
+        if f.endswith('.html'):
+            s = read(os.path.join(root, f))
+            for pat in (r"{%\s*extends\s*['\"]([^'\"]+)['\"]",
+                        r"{%\s*include\s*['\"]([^'\"]+)['\"]",
+                        r"{%\s*import\s*['\"]([^'\"]+)['\"]",
+                        r"render_template\(\s*['\"]([^'\"]+)['\"]"):
+                refs |= set(re.findall(pat, s))
+
+all_tpl = []
+for root, dirs, files in os.walk(TPL):
+    for f in files:
+        if f.endswith('.html'):
+            all_tpl.append(os.path.relpath(os.path.join(root, f), TPL))
+
+referenced = rendered | refs
+orphans = []
+for t in sorted(all_tpl):
+    base = os.path.basename(t)
+    if t in referenced or base in referenced:
+        continue
+    # macro/library files are referenced dynamically sometimes
+    orphans.append(t)
+
+print(f'templates total     : {len(all_tpl)}')
+print(f'referenced          : {len([t for t in all_tpl if t not in orphans])}')
+print(f'ORPHAN templates    : {len(orphans)}')
+print()
+for o in orphans:
+    lines = len(read(os.path.join(TPL, o)).splitlines())
+    print(f'   ✗ {o:<58} {lines} lines')