fix: resolve hardcoded /app paths and loosen mediapipe pin for native installs

Path resolution for the feature manifest and install script was hardcoded
to /app/..., which only works inside the Docker container. Native installs
(e.g. Proxmox at /opt/snapotter) hit "No such file or directory" errors.

Resolve both paths relative to the source file location via import.meta.url
so they work regardless of where the project is installed.

Also loosen mediapipe==0.10.21 to >=0.10.21 in requirements.txt and
requirements-gpu.txt to match the feature manifest. The exact pin has no
cp313 wheel, so it fails on Python 3.13 (Debian 13 default). mediapipe
0.10.35 ships py3-none universal wheels that resolve cleanly.

Reported-by: MickLesk (community-scripts/ProxmoxVE#14720)

packages/ai/python/requirements-gpu.txt

@@ -2,7 +2,7 @@ rembg==2.0.62
 realesrgan==0.3.0
 paddleocr==2.9.1
 paddlepaddle-gpu==3.0.0
-mediapipe==0.10.21
+mediapipe>=0.10.21
 onnxruntime-gpu==1.20.1
 numpy==1.26.4
 Pillow==11.1.0

packages/ai/python/requirements.txt

@@ -2,7 +2,7 @@ rembg[cpu]==2.0.62
 realesrgan==0.3.0
 paddleocr[doc-parser]>=3.4.0,<3.5.0
 paddlepaddle>=3.0.0,<3.1.0
-mediapipe==0.10.21
+mediapipe>=0.10.21
 onnxruntime==1.20.1
 numpy==1.26.4
 Pillow==11.1.0