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/api/src/openapi.yaml

@@ -1,9 +1,9 @@
 openapi: 3.1.0
 info:
-  title: Stirling Image API
+  title: ashim API
   version: 0.9.0
   description: |
-    REST API for Stirling Image, a self-hosted image processing platform with 30+ tools.
+    REST API for ashim, a self-hosted image processing platform with 30+ tools.
 
     ## Authentication
 
@@ -16,7 +16,7 @@ info:
     Endpoints marked with a lock icon require authentication. Admin-only endpoints are noted in their description.
   license:
     name: AGPL-3.0
-    url: https://github.com/stirling-image/stirling-image/blob/main/LICENSE
+    url: https://github.com/ashim-hq/ashim/blob/main/LICENSE
 
 servers:
   - url: /