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/api/src/index.ts

@@ -23,14 +23,6 @@ import { teamsRoutes } from "./routes/teams.js";
 import { registerToolRoutes } from "./routes/tools/index.js";
 import { userFileRoutes } from "./routes/user-files.js";
 
-// Warn about deprecated STIRLING_VARIANT env var
-if (process.env.STIRLING_VARIANT) {
-  console.warn(
-    `WARNING: STIRLING_VARIANT="${process.env.STIRLING_VARIANT}" is set but ignored. ` +
-      "There is now a single unified image with all features. Remove STIRLING_VARIANT from your environment.",
-  );
-}
-
 // Run before anything else
 runMigrations();
 console.log("Database initialized");