refactor: remove lite variant, fix release workflow

- Remove all lite/full variant logic from frontend, API, shared constants,
  docs, and tests (single unified Docker image only)
- Replace single QEMU multi-arch Docker build with per-architecture native
  builds (amd64 + arm64) and manifest merge to fix disk space exhaustion
- Add disk cleanup step and per-platform build cache scopes
- Switch release trigger from push to workflow_dispatch
- Add GitHub issue templates and PR template

apps/docs/.vitepress/config.mts

@@ -46,7 +46,7 @@ export default defineConfig({
 `,
         customTemplateVariables: {
           description:
-            "Self-hosted, open-source image processing platform with 30+ tools. Runs in a single Docker container. Available as :latest (full, ~11 GB with AI/ML) or :lite (~1.5 GB, image processing only).",
+            "Self-hosted, open-source image processing platform with 30+ tools including AI/ML. Runs in a single Docker container with GPU auto-detection.",
           details:
             "Resize, compress, convert, remove backgrounds, upscale, run OCR, and more - without sending images to external services.",
         },