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

packages/shared/src/constants.ts

@@ -374,8 +374,7 @@ export const APP_VERSION = "1.11.0";
 
 /**
  * Tool IDs that require the Python sidecar (AI/ML tools).
- * Used by the API to register 501 stubs in lite mode,
- * and by the frontend for progress/timeout behavior.
+ * Used by the frontend for progress/timeout behavior.
  */
 export const PYTHON_SIDECAR_TOOLS = [
   "remove-background",