chore: rename Stirling-Image to ashim across entire codebase

Complete rebrand from Stirling-Image to ashim following the project
move to https://github.com/ashim-hq/ashim.

Changes across 117 files:
- Package scope: @stirling-image/* → @ashim/*
- GitHub URLs: stirling-image/stirling-image → ashim-hq/ashim
- Docker Hub: stirlingimage/stirling-image → ashimhq/ashim
- GitHub Pages: stirling-image.github.io → ashim-hq.github.io
- All branding text: "Stirling Image" → "ashim"
- Docker service/volumes/user: stirling → ashim
- Database: stirling.db → ashim.db
- localStorage keys: stirling-token → ashim-token
- Environment variables: STIRLING_GPU → ASHIM_GPU
- Python cache dirs: .cache/stirling-image → .cache/ashim
- SVG filter IDs, test prefixes, and all other references

packages/ai/python/gpu.py

@@ -7,7 +7,7 @@ import os
 def gpu_available():
     """Return True if a usable CUDA GPU is present at runtime."""
     # Allow explicit disable via env var (set to "false" or "0")
-    override = os.environ.get("STIRLING_GPU")
+    override = os.environ.get("ASHIM_GPU")
     if override is not None and override.lower() in ("0", "false", "no"):
         return False