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/routers/images.py

@@ -0,0 +1,81 @@
+from fastapi import APIRouter, HTTPException, Depends
+from fastapi.responses import FileResponse
+from sqlalchemy.orm import Session
+from pathlib import Path
+
+from app.database import get_db
+from app.models.project import Project
+from app.services.edit_service import EditService
+
+router = APIRouter(prefix="/projects", tags=["images"])
+
+
+@router.get("/{project_id}/original")
+def get_original_image(
+    project_id: int,
+    db: Session = Depends(get_db)
+):
+    """Get the original uploaded image"""
+    project = db.query(Project).filter(Project.id == project_id).first()
+    if not project:
+        raise HTTPException(status_code=404, detail="Project not found")
+
+    edit_service = EditService()
+    image_path = edit_service.get_original_image_path(project_id)
+
+    if not image_path.exists():
+        raise HTTPException(status_code=404, detail="Original image not found")
+
+    return FileResponse(
+        image_path,
+        media_type="image/png",
+        headers={"Cache-Control": "public, max-age=3600"}
+    )
+
+
+@router.get("/{project_id}/current")
+def get_current_image(
+    project_id: int,
+    db: Session = Depends(get_db)
+):
+    """Get the current edited image"""
+    project = db.query(Project).filter(Project.id == project_id).first()
+    if not project:
+        raise HTTPException(status_code=404, detail="Project not found")
+
+    edit_service = EditService()
+    image_path = edit_service.get_current_image_path(project_id)
+
+    if not image_path.exists():
+        raise HTTPException(status_code=404, detail="Current image not found")
+
+    return FileResponse(
+        image_path,
+        media_type="image/png",
+        headers={"Cache-Control": "no-cache"}
+    )
+
+
+@router.get("/{project_id}/history/{edit_id}/result")
+def get_edit_result(
+    project_id: int,
+    edit_id: int,
+    db: Session = Depends(get_db)
+):
+    """Get the result image from a specific edit"""
+    project = db.query(Project).filter(Project.id == project_id).first()
+    if not project:
+        raise HTTPException(status_code=404, detail="Project not found")
+
+    edit_service = EditService()
+    edit_dir = edit_service.get_edit_dir(project_id, edit_id)
+    result_path = edit_dir / "result.png"
+
+    if not result_path.exists():
+        raise HTTPException(status_code=404, detail="Edit result not found")
+
+    return FileResponse(
+        result_path,
+        media_type="image/png",
+        headers={"Cache-Control": "public, max-age=3600"}
+    )