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/unit/image-engine/operations.test.ts

@@ -34,7 +34,7 @@ import {
   saturation,
   sepia,
   stripMetadata,
-} from "@stirling-image/image-engine";
+} from "@ashim/image-engine";
 
 const FIXTURES_DIR = path.resolve(__dirname, "../../fixtures");
 
@@ -1395,7 +1395,7 @@ describe("parseExif", () => {
     const result = parseExif(metadata.exif!);
     expect(result.image.Artist).toBe("Test Artist");
     expect(result.image.Copyright).toBe("2026 Test Copyright");
-    expect(result.image.Software).toBe("Stirling-Image Test");
+    expect(result.image.Software).toBe("ashim Test");
     expect(result.image.ImageDescription).toBe("Test Description");
   });
 
@@ -1489,7 +1489,7 @@ describe("editMetadata", () => {
     expect(parsed.Image?.Artist).toBe("New Artist");
     expect(parsed.Image?.Copyright).toBe("New Copyright");
     // Original fields should be preserved via withExifMerge
-    expect(parsed.Image?.Software).toBe("Stirling-Image Test");
+    expect(parsed.Image?.Software).toBe("ashim Test");
   });
 
   it("clears GPS while preserving other EXIF", async () => {