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/cli/src/commands/daemon/runtime-toolchain.ts

@@ -84,7 +84,7 @@ async function resolveNodePathFromPidWindows(pid: number): Promise<NodePathFromP
         error: errors.join("; ") || "could not resolve executable path from PID",
       };
     }
-    const probe = probes[index] as (typeof probes)[number];
+    const probe = probes[index];
     const result = await runProcessProbe(probe.command, probe.args);
     if (result.resolved) {
       const resolved = probe.parseValue ? probe.parseValue(result.resolved) : result.resolved;