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/settings.spec.ts

@@ -76,7 +76,7 @@ test.describe("Settings Dialog", () => {
     await page.getByText("About").click();
 
     // Should show app description
-    await expect(page.getByText(/stirling image|privacy|self-hosted/i).first()).toBeVisible();
+    await expect(page.getByText(/ashim|privacy|self-hosted/i).first()).toBeVisible();
   });
 
   test("System Settings section has configuration", async ({ loggedInPage: page }) => {