fix: render pipeline + multi-tenancy bugs (B-Fix-1 through B-Fix-9)

- Remove worker-thumbnail (no Blender, was competing on thumbnail_rendering)
- Move render_order_line_task to thumbnail_rendering queue (render-worker)
- Restore template_service.py real implementation (fix circular import shim)
- Thread tenant_id through STEP upload, Excel import, product create
- Make system tables (output_types, materials, etc.) tenant_id nullable
- Fix tenants frontend 307-redirect: use trailing slash /tenants/
- Remove Flamenco + Three.js from Admin UI (unsupported)
- Set all output_types render_backend to celery (was flamenco)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/services/template_service.py

@@ -1,3 +1,102 @@
-# Compat shim — use app.domains.rendering.service instead
-from app.domains.rendering.service import resolve_template, get_material_library_path
-__all__ = ["resolve_template", "get_material_library_path"]
+"""Render template resolution service.
+
+Used from Celery tasks (sync context) to find the best matching .blend template
+for a given category + output type combination.
+
+Cascade priority (first active match wins):
+1. Exact:         category_key + output_type_id
+2. Category only: category_key + output_type_id IS NULL
+3. OT only:       category_key IS NULL + output_type_id
+4. Global:        both NULL
+5. No template  → caller falls back to factory-settings behavior
+"""
+import logging
+
+from sqlalchemy import create_engine, select, and_
+from sqlalchemy.orm import Session
+
+from app.models.render_template import RenderTemplate
+from app.models.system_setting import SystemSetting
+
+logger = logging.getLogger(__name__)
+
+_engine = None
+
+
+def _get_engine():
+    global _engine
+    if _engine is None:
+        from app.config import settings as app_settings
+        _engine = create_engine(app_settings.database_url_sync)
+    return _engine
+
+
+def resolve_template(
+    category_key: str | None = None,
+    output_type_id: str | None = None,
+) -> RenderTemplate | None:
+    """Find the best matching active render template.
+
+    Uses sync SQLAlchemy — safe for Celery tasks.
+    """
+    engine = _get_engine()
+    with Session(engine) as session:
+        active = RenderTemplate.is_active == True  # noqa: E712
+
+        # 1. Exact match
+        if category_key and output_type_id:
+            row = session.execute(
+                select(RenderTemplate).where(and_(
+                    active,
+                    RenderTemplate.category_key == category_key,
+                    RenderTemplate.output_type_id == output_type_id,
+                ))
+            ).scalar_one_or_none()
+            if row:
+                return row
+
+        # 2. Category only
+        if category_key:
+            row = session.execute(
+                select(RenderTemplate).where(and_(
+                    active,
+                    RenderTemplate.category_key == category_key,
+                    RenderTemplate.output_type_id.is_(None),
+                ))
+            ).scalar_one_or_none()
+            if row:
+                return row
+
+        # 3. OT only
+        if output_type_id:
+            row = session.execute(
+                select(RenderTemplate).where(and_(
+                    active,
+                    RenderTemplate.category_key.is_(None),
+                    RenderTemplate.output_type_id == output_type_id,
+                ))
+            ).scalar_one_or_none()
+            if row:
+                return row
+
+        # 4. Global fallback (both NULL)
+        row = session.execute(
+            select(RenderTemplate).where(and_(
+                active,
+                RenderTemplate.category_key.is_(None),
+                RenderTemplate.output_type_id.is_(None),
+            ))
+        ).scalar_one_or_none()
+        return row
+
+
+def get_material_library_path() -> str | None:
+    """Read material_library_path from system_settings. Returns None if empty."""
+    engine = _get_engine()
+    with Session(engine) as session:
+        row = session.execute(
+            select(SystemSetting).where(SystemSetting.key == "material_library_path")
+        ).scalar_one_or_none()
+        if row and row.value and row.value.strip():
+            return row.value.strip()
+        return None