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/shared/src/i18n/en.ts

@@ -194,7 +194,7 @@ export const en = {
     regenerateKey: "Regenerate",
     copyKey: "Copy Key",
     aboutDescription:
-      "Stirling Image is a self-hosted, privacy-first image processing suite with 30+ tools.",
+      "ashim is a self-hosted, privacy-first image processing suite with 30+ tools.",
     aboutLinks: "Links",
     github: "GitHub",
     documentation: "Documentation",