Share Real-Debrid and TorBox folder sorting

[ghbarker]

Real-Debrid and TorBox download screens duplicate the same folder ordering and tree-building logic. Move those three unchanged method bodies into CloudFolderSort and route both screens through it, preserving numeric ordering, tie behavior and existing handling of non-numbered names.

Based independently on webdav-sync at 077f2e79. The helper uses the existing RDFileNode; no provider registry, shared screen state machine or other refactor is required.

Validation with Flutter 3.44.8 / Dart 3.12.2: the two public-screen tests pass on the original and extracted implementations; four additional helper tests pass. Original-body comparison and all redirected host calls were checked. Changed-path analysis has the same 72 existing diagnostics as upstream, with none added. No device playback or full device build is claimed.

Independent adversarial review found no production regressions. The final branch passes 12 tests after adding tie-collision and larger-cohort ordering coverage; mutations that introduced numeric-name tiebreakers or stable-sort behavior were rejected. Supplemental-test analysis is clean; the existing production analysis baseline above is unchanged.

Combined validation with the other ten proposed slices: 304 focused/integration tests passed and an Android release build succeeded with Flutter 3.44.8 / Dart 3.12.2 / JDK 17. The test and build source trees match. The existing Windows Spotlight golden is excluded from that selection. A separate clean upstream full-suite run has 6,044 passes, 12 skips, 55 failing user tests and one failing teardown hook; this is not a full-suite or GitHub CI pass. Physical-device validation of the upstream ports remains outstanding.