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

tests/e2e/rbac.spec.ts

@@ -144,7 +144,7 @@ base.describe("RBAC - User sees restricted tabs", () => {
     await login(page, TEST_USER, TEST_PASSWORD);
 
     // Extract token from localStorage
-    const token = await page.evaluate(() => localStorage.getItem("stirling-token"));
+    const token = await page.evaluate(() => localStorage.getItem("ashim-token"));
     expect(token).toBeTruthy();
     const bearerToken = token as string;