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/app/src/utils/agent-directory-sync.ts

@@ -1,9 +1,9 @@
-import type { FetchAgentHistoryEntry, FetchAgentsEntry } from "@server/client/daemon-client";
+import type { FetchAgentsEntry } from "@server/client/daemon-client";
 import { type Agent, useSessionStore } from "@/stores/session-store";
 import { derivePendingPermissionKey, normalizeAgentSnapshot } from "@/utils/agent-snapshots";
 import { resolveProjectPlacement } from "@/utils/project-placement";
 
-type AgentDirectoryFetchEntry = FetchAgentsEntry | FetchAgentHistoryEntry;
+type AgentDirectoryFetchEntry = FetchAgentsEntry;
 
 interface PendingPermissionEntry {
   key: string;

packages/app/src/utils/agent-snapshots.ts

@@ -1,4 +1,3 @@
-import type { AgentLifecycleStatus } from "@server/shared/agent-lifecycle";
 import type { AgentSnapshotPayload } from "@server/shared/messages";
 import type { AgentPermissionRequest } from "@server/server/agent/agent-sdk-types";
 
@@ -31,7 +30,7 @@ export function normalizeAgentSnapshot(snapshot: AgentSnapshotPayload, serverId:
     serverId,
     id: snapshot.id,
     provider: snapshot.provider,
-    status: snapshot.status as AgentLifecycleStatus,
+    status: snapshot.status,
     createdAt,
     updatedAt,
     lastUserMessageAt,

packages/app/src/utils/os-notifications.test.ts

@@ -148,7 +148,7 @@ describe("sendOsNotification", () => {
     clicked.clickListeners[0]?.({} as Event);
 
     expect(dispatchEvent).toHaveBeenCalledTimes(1);
-    const event = dispatchEvent.mock.calls[0]?.[0] as unknown as {
+    const event = dispatchEvent.mock.calls[0]?.[0] as {
       type?: string;
       detail?: { data?: Record<string, unknown> };
     };

packages/app/src/utils/os-notifications.ts

@@ -132,7 +132,7 @@ function dispatchWebNotificationClick(detail: WebNotificationClickDetail): boole
       cancelable: true,
     },
   );
-  return dispatch(event) === false;
+  return !dispatch(event);
 }
 
 function fallbackNavigateToNotificationTarget(data: Record<string, unknown> | undefined): void {