fix(client): clean up leftover pre-TerminalView dead code and type errors in Workspace.tsx

`npm run test:client` (Vitest/esbuild) doesn't type-check, so several
tasks' incomplete cleanup of the old RunConsole-era code in
Workspace.tsx (SlashCommand/BUILTIN_SLASH_COMMANDS references, old
RunStatus values, a stray `mode` field, a wrong `prompt` vs
`initialPrompt` key) went unnoticed through every review until `tsc
--noEmit` was run directly. Also fixes a stale `RunStatusPayload.exitCode`
read in Tabby's brain.ts and dangling RunStreamPayload/RunInputAckPayload
references left in types.ts.

client/src/components/Tabby/__tests__/brain.test.ts

@@ -167,26 +167,11 @@ describe("reduceTabby counts and pulses", () => {
     expect(ok.state.worriedUntil).toBe(0);
   });
 
-  it("run_status completed exit 0 is happy, nonzero/error/killed is worried", () => {
-    const good = reduceTabby(
-      initialTabbyState(T0),
-      runStatusMsg({ status: "completed", exitCode: 0 }),
-      T0
-    );
-    expect(good.pulse).toBe("run_done");
-    expect(deriveMood(good.state, T0)).toBe("happy");
-    const bad = reduceTabby(
-      initialTabbyState(T0),
-      runStatusMsg({ status: "completed", exitCode: 1 }),
-      T0
-    );
-    expect(bad.pulse).toBe("error");
-    const err = reduceTabby(initialTabbyState(T0), runStatusMsg({ status: "error" }), T0);
-    expect(err.pulse).toBe("error");
-    const killed = reduceTabby(initialTabbyState(T0), runStatusMsg({ status: "killed" }), T0);
-    expect(killed.pulse).toBe("error");
+  it("run_status updates activity timestamp only (no exit code available)", () => {
     const running = reduceTabby(initialTabbyState(T0), runStatusMsg({ status: "running" }), T0);
     expect(running.pulse).toBe(null);
+    const gone = reduceTabby(initialTabbyState(T0), runStatusMsg({ status: "gone" }), T0);
+    expect(gone.pulse).toBe(null);
   });
 
   it("any handled message refreshes lastActivityAt", () => {