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

.github/pull_request_template.md

@@ -1,12 +1,12 @@
 <!--
-Thanks for your interest in Stirling Image.
+Thanks for your interest in ashim.
 
 We don't accept pull requests. All development is handled internally to maintain architectural consistency and code quality.
 
 If you've found a bug or have a feature idea, please open an issue instead:
-https://github.com/stirling-image/stirling-image/issues
+https://github.com/ashim-hq/ashim/issues
 
 Your feedback is valuable and directly shapes the project.
 -->
 
-**This project does not accept pull requests.** Please close this PR and [open an issue](https://github.com/stirling-image/stirling-image/issues/new/choose) instead. See [CONTRIBUTING.md](CONTRIBUTING.md) for details.
+**This project does not accept pull requests.** Please close this PR and [open an issue](https://github.com/ashim-hq/ashim/issues/new/choose) instead. See [CONTRIBUTING.md](CONTRIBUTING.md) for details.