Move ai-stack and paintplus vendored source under vendor/

Matches the existing vendor/easy-asterisk convention (used by
services/asterisk.sh) instead of two one-off top-level directories that
cluttered the repo root and didn't look like anything else next to
setup.sh, lib/, services/, extras/. Only the two services' own SRC_DIR
path resolution and header comments needed updating — nothing else in
the repo referenced the old ./ai-stack / ./paintplus paths.

Also documents vendor/ in README.md's Layout section.

vendor/paintplus/backend/app/models/patch.py

@@ -0,0 +1,37 @@
+from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, Text, Boolean
+from sqlalchemy.orm import relationship
+from datetime import datetime
+from app.database import Base
+
+
+class Patch(Base):
+    __tablename__ = "patches"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
+    name = Column(String, nullable=False)
+    description = Column(Text, nullable=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+
+    # Source information
+    source_type = Column(String, nullable=False)  # "ai_generated", "manual_selection", "imported"
+    source_project_id = Column(Integer, ForeignKey("projects.id"), nullable=True)
+    source_edit_id = Column(Integer, ForeignKey("edits.id"), nullable=True)
+
+    # Patch metadata
+    width = Column(Integer, nullable=False)
+    height = Column(Integer, nullable=False)
+    tags = Column(Text, nullable=True)  # Comma-separated tags
+    category = Column(String, nullable=True)  # "hand", "face", "body", "object", "texture", etc.
+
+    # Is this patch shared/public?
+    is_public = Column(Boolean, default=False)
+
+    # File path (relative to data dir)
+    file_path = Column(String, nullable=False)
+    thumbnail_path = Column(String, nullable=True)
+
+    # Relationships
+    user = relationship("User", back_populates="patches")
+    source_project = relationship("Project")
+    source_edit = relationship("Edit")