ci(lotus): hard-gate lint, format and unit tests before build; add concurrency

The workflow only built and smoke-checked that dist/index.html existed,
so a type error, lint violation or failing test could be tagged straight
to a published npm release. Run `pnpm lint` (tsc + oxlint + knip),
`pnpm format:check` (oxfmt) and `pnpm test:unit --run` before the build,
all hard. Add the same cancel-in-progress concurrency group cinny's CI
uses so rapid pushes to lotus don't queue redundant full builds.

Also fixes the one tsc error the v0.25.0 merge surfaced in
lotusDecorations (lazyActions.off now returns the emitter), so the new
gate is green from its first run.

Fixes #5
Fixes #34

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/lotus/lotusDecorations.ts

@@ -84,8 +84,9 @@ export function startLotusDecorations(): () => void {
       emit();
     };
     w.lazyActions.on(LotusWidgetActions.Decorations, handler);
-    unregister = (): void =>
+    unregister = (): void => {
       w.lazyActions.off(LotusWidgetActions.Decorations, handler);
+    };
   }
   registrations += 1;