upgrade: adopt V8.21.3 (V8.13→8.21.3: P5 SFTP/S3, P6 multilingual, editor overhaul, enterprise hardening)

Overlay ~150 upstream items onto our V8.12 base, preserving trade-pro
theme, registry tests, and design docs. Re-applied our patch set
(discovery/env_for/blocks.css/type-mapping/theme_color/frontend entries,
test_theme_pro_v3 mods) — all anchors survived upstream evolution.

New platform enhancement (fixes upgrade-introduced regression):
multilingual.site_locale now honors settings_json.locale, plus
PUT /api/i18n/sites/{id}/locale — standalone English sites get
<html lang='en'> under the V8.15 locale-rewrite pipeline.

compose: adopt V8.21.3 (image 8.21.3-dev.1, /api/ready probes, MySQL/S3
env) with project name pinned to siteforge-v8-10 (data volumes).

Tests: 356 passed / 11 failed — all 11 confirmed pre-existing in
pristine V8.21.3 on this host (10 upstream Windows env + our build test
now green after locale fix). Patch registry updated in plan doc.

Co-Authored-By: Claude Code <noreply@anthropic.com>

app/core.py

@@ -4,12 +4,12 @@ import json
 import re
 import socket
 import uuid
-from pathlib import Path
 from urllib.parse import urlparse, unquote
 import bleach
 from . import db
 
-ROOT = Path(__file__).resolve().parent.parent
+TYPES = ('page','product','post','service','case','brand','vehicle','other')
+ROOT = __import__('pathlib').Path(__file__).resolve().parent.parent
 
 def discover_themes():
     """Discover built-in themes from themes/*/manifest.json (single source of truth)."""
@@ -29,7 +29,6 @@ def discover_themes():
             found.append(entry.name)
     return tuple(found)
 
-TYPES = ('page','product','post','service','case','brand','vehicle','other')
 THEMES = discover_themes()
 ALLOWED_TAGS = ['p','br','b','i','u','em','strong','h1','h2','h3','h4','h5','h6','ul','ol','li','blockquote','pre','code','a','img','figure','figcaption','table','thead','tbody','tr','th','td','hr','div','span']
 ALLOWED_ATTRS = {'a':['href','title','target','rel'], 'img':['src','alt','title','loading','width','height'], 'td':['colspan','rowspan'], 'th':['colspan','rowspan']}