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/enterprise.py

@@ -134,7 +134,11 @@ def create_user(request:Request,payload:UserCreate):
         person=uid()
         db.insert('INSERT INTO team_users(id,username,password_hash,display_name,created_at) VALUES (?,?,?,?,?)',
                   (person,payload.username,hash_password(payload.password),payload.display_name,db.now()))
-    except sqlite3.IntegrityError:raise HTTPException(409,'用户名已存在')
+    except Exception as exc:
+        # PostgreSQL uses psycopg.errors.UniqueViolation rather than sqlite3.IntegrityError.
+        if isinstance(exc,sqlite3.IntegrityError) or getattr(exc,'sqlstate',None)=='23505':
+            raise HTTPException(409,'用户名已存在') from exc
+        raise
     return {'id':person,'username':payload.username,'display_name':payload.display_name}
 
 @router.patch('/team/users/{user_id}/disable')