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/theme_pro.py

@@ -16,15 +16,15 @@ from markupsafe import Markup
 from .core import sanitize, route_path, THEMES
 
 ROOT=Path(__file__).resolve().parent.parent
+LOADER=Environment(loader=FileSystemLoader(str(ROOT/'themes')),autoescape=select_autoescape(['html','xml']))
+
 _ENVS={}
 
 def env_for(theme):
     """Per-theme Jinja env: theme dir first, shared themes/ root as fallback.
 
     Lets a theme override shared macros (_professional_components.html) while
-    inheriting everything else. Cached: one env per theme across large builds.
-    Only built-in theme names are accepted; callers are expected to enforce the
-    THEMES whitelist too (render does), this is defense in depth.
+    inheriting everything else. Cached per theme; degraded envs are not cached.
     """
     if theme not in THEMES:raise ValueError('未知主题')
     env=_ENVS.get(theme)
@@ -33,7 +33,7 @@ def env_for(theme):
         canonical=theme_dir.is_dir()
         search=[str(theme_dir),str(ROOT/'themes')] if canonical else [str(ROOT/'themes')]
         env=Environment(loader=FileSystemLoader(search),autoescape=select_autoescape(['html','xml']))
-        if canonical:_ENVS[theme]=env  # degraded envs are not cached
+        if canonical:_ENVS[theme]=env
     return env
 
 TITLES={'product':'产品中心','vehicle':'车型中心','post':'新闻资讯','case':'项目案例','brand':'品牌中心','service':'服务与解决方案'}
@@ -189,6 +189,7 @@ def make_context(site,page,records,mode='detail',listing_items=None,prepared=Non
             'features':groups['service'][:3], 'stories':groups['post'][:3], 'cases':groups['case'][:3],
             'brands':assets['brands'],'categories':assets['categories'], 'nav':nav,
             'chrome':chrome,'chrome_is_custom':bool(settings.get('site_design')),
+            'mobile_tab_icons':{'home':'⌂','grid':'▦','products':'▤','news':'☷','contact':'✉','phone':'☎','info':'ⓘ','search':'⌕','menu':'☰','star':'☆'},
             'footer_nav':nav if chrome['footer']['show_nav'] else [],'specs':spec,
             'related':related,'fields':detail_fields,'content':Markup(sanitize(pg.get('body') or '')),
             'title':title, 'seo_title':pg.get('seo_title') or title,'seo_description':pg.get('seo_description') or pg.get('summary') or site.get('tagline') or '',