feat(fs): W4-E4 fsproxy hang isolation, partial sweep, replace-with-verify, TIMEOUT retry

- adapters/fs: FsProxy + fsworker run each file op in a killable subprocess;
  progress-stall watchdog (FS_HANG_TIMEOUT_MS) for copy/hash, total timeout for
  quick ops; SIGTERM -> SIGKILL -> FsError('TIMEOUT'); stat/checkRoot timeouts
  never read as missing
- copyWithVerify: onExisting conflict/skip/replace (hardlink backup + atomic
  rename, old file to .umt-trash or deleted), sweep stale partials before write,
  document why permissions/owner are not copied
- filesMatch/filesMatchSha256 throw FsError on read failure instead of
  match=false; crossDeviceMove skips redundant re-hash after sha256 copy
- FsErrorCode TIMEOUT + fsErrorClass; organize executeRecord routes fs ops
  through fsproxy, retries TIMEOUT/IO up to FS_TRANSFER_MAX_ATTEMPTS then opens
  a decision without deleting the record; reconcile errors no longer reported
  as EEXIST
- domain: subtitle .default marker (ORGANIZE_DEFAULT_SUBTITLE_LANG) and
  findOtherVersions (same season/episode/part, video only) as upgrade
  disposal candidates
- scripts/bench/fs-bench.ts and benchmark record in porting doc

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/domain/src/organize/index.ts

@@ -13,4 +13,5 @@ export {
   planOrganize,
   type SourceFile,
 } from "./plan.ts";
-export { sidecarLanguageSuffix, sidecarStem } from "./sidecars.ts";
+export { type DefaultSubtitleLang, sidecarLanguageSuffix, sidecarStem } from "./sidecars.ts";
+export { findOtherVersions } from "./versions.ts";