feat: GPU rendering + material matching + perf improvements

- GPU: fix Cycles device activation order — set compute_device_type
  BEFORE engine init, re-set AFTER open_mainfile wipes preferences
- GPU: remove _mark_sharp_and_seams edit-mode loop (redundant with
  Blender 5.0 shade_smooth_by_angle), saves ~200s/render on 175 parts
- Material: fix _AFN suffix mismatch — build AF-stripped mat_map keys
  and add prefix fallback in _apply_material_library (blender_render.py)
- Material: production GLB now uses get_material_library_path() which
  checks active AssetLibrary instead of empty legacy system setting
- Admin: RenderTemplateTable multi-select output types (M2M frontend)
- Admin: MaterialLibraryPanel replaced with link to Asset Libraries
- UX: move Toaster to top-left to avoid dispatch button overlap
- SQLAlchemy: add .unique() to all RenderTemplate M2M collection queries
- Logging: flush=True on all Blender progress prints, stdout reconfigure

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

backend/app/domains/rendering/models.py

@@ -1,10 +1,19 @@
 import uuid
 from datetime import datetime
-from sqlalchemy import String, DateTime, Boolean, Text, Integer, Float, ForeignKey
+from sqlalchemy import String, DateTime, Boolean, Text, Integer, Float, ForeignKey, Table, Column
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from sqlalchemy.dialects.postgresql import UUID, JSONB
 from app.database import Base
 
+
+# M2M: render templates ↔ output types
+render_template_output_types = Table(
+    "render_template_output_types",
+    Base.metadata,
+    Column("template_id", UUID(as_uuid=True), ForeignKey("render_templates.id", ondelete="CASCADE"), primary_key=True),
+    Column("output_type_id", UUID(as_uuid=True), ForeignKey("output_types.id", ondelete="CASCADE"), primary_key=True),
+)
+
 VALID_RENDER_BACKENDS = {"celery"}
 
 
@@ -66,7 +75,10 @@ class RenderTemplate(Base):
     created_at: Mapped[datetime] = mapped_column(DateTime, nullable=False, server_default="now()")
     updated_at: Mapped[datetime] = mapped_column(DateTime, nullable=False, server_default="now()", onupdate=datetime.utcnow)
 
+    # Legacy single FK (kept for backward compat, prefer output_types M2M)
     output_type = relationship("OutputType", lazy="joined")
+    # M2M: multiple output types per template
+    output_types = relationship("OutputType", secondary=render_template_output_types, lazy="joined")
 
 
 class ProductRenderPosition(Base):