Clean workspace (make it match the depot)

- Actions -> Clean workspace: preview extra/deleted/modified files, then apply
  p4 clean (opened files untouched)
- Backend p4 clean -n / clean

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/p4.ts

@@ -72,6 +72,8 @@ export const p4 = {
   switchStream: (stream: string) => invoke<P4Info>("p4_switch_stream", { stream }),
   streamInteg: (stream: string, direction: "down" | "up") => invoke<string>("p4_stream_integ", { stream, direction }),
   filelog: (depot: string) => invoke<Record<string, unknown>>("p4_filelog", { depot }),
+  cleanPreview: (scope = "") => invoke<OpenedFile[]>("p4_clean_preview", { scope }),
+  cleanApply: (scope = "") => invoke<string>("p4_clean_apply", { scope }),
   jobs: () => invoke<{ Job?: string; Status?: string; Description?: string; User?: string; [k: string]: unknown }[]>("p4_jobs"),
   fix: (job: string, change: string) => invoke<string>("p4_fix", { job, change }),
   jobSpec: (job: string) => invoke<string>("p4_job_spec", { job }),