Remove unnecessary type assertions across codebase

Add oxlint-tsgolint and configure typescript/no-unnecessary-type-assertion
to flag redundant `!` and `as Foo` casts. Type-aware mode is left off by
default to keep `npm run lint` fast; the rule sits configured for when we
turn type-aware on intentionally. Auto-fix removed ~283 redundant casts;
two manual touch-ups: a real tsgolint false positive in split-container.tsx
and a stale ChildProcess import after a double-cast collapsed.

packages/server/src/client/daemon-client-runtime-metrics.ts

@@ -138,7 +138,7 @@ export class DaemonClientRuntimeMetrics {
 
   private pruneBuckets(now: number): void {
     const cutoff = now - this.windowMs;
-    while (this.buckets.length > 0 && this.buckets[0]!.endedAt < cutoff) {
+    while (this.buckets.length > 0 && this.buckets[0].endedAt < cutoff) {
       this.buckets.shift();
     }
   }