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/lib/types.ts

@@ -1647,9 +1647,7 @@ export interface WSMessage {
     | DashboardEvent
     | ImportProgressMessage
     | UpdateStatusPayload
-    | RunStreamPayload
     | RunStatusPayload
-    | RunInputAckPayload
     | CcConfigChangedPayload
     | AlertEvent
     | WorkflowRun