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

apps/web/public/logo.svg

@@ -10,6 +10,5 @@
     <line x1="40" y1="48" x2="100" y2="48" stroke="#3b82f6" stroke-width="1.5" opacity="0.4"/>
   </g>
   <!-- Wordmark -->
-  <text x="56" y="30" font-family="-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif" font-weight="700" font-size="24" letter-spacing="-0.5" fill="#0f172a">Stirling </text>
-  <text x="160" y="30" font-family="-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif" font-weight="700" font-size="24" letter-spacing="-0.5" fill="#3b82f6">Image</text>
+  <text x="56" y="30" font-family="-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif" font-weight="700" font-size="24" letter-spacing="-0.5" fill="#3b82f6">ashim</text>
 </svg>