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/ISSUE_TEMPLATE/config.yml

@@ -1,8 +1,8 @@
 blank_issues_enabled: false
 contact_links:
   - name: Documentation
-    url: https://stirling-image.github.io/stirling-image/
+    url: https://ashim-hq.github.io/ashim/
     about: Check the docs for setup guides, configuration, and API reference.
   - name: Security vulnerability
-    url: https://github.com/stirling-image/stirling-image/security/advisories/new
+    url: https://github.com/ashim-hq/ashim/security/advisories/new
     about: Report security issues privately through GitHub Security Advisories.