fix(newos4): four phone-test defects — no preview close, single-file share, dead-end fullscreen, silent WebDAV move

All four came from the operator's phone pass on v4.6.95 and each collapsed to a line of code.

A "No file selected to download": the preview pane had no close control; the only ✕ was the file
  manager's own, and it calls _closeOverlay() which wipes _multiSelect/_selectedFile/_selectMode.
  On a phone the preview covers the list, so closing it before pressing Download always emptied the
  selection. The toolbar now starts with ✕ -> _clearPreview(), which keeps the selection and leaves
  fullscreen first; Download with no targets names the fix instead of stating a dead end.
B share/copy: 🔗 existed only in the preview toolbar and took a single path, and after the Android
  share sheet there was no copy affordance. Added _sharePaths(paths, mode) used by both the toolbar
  (1 path, 📋 copy and 🔗 share) and a new action-bar 🔗 Share (whole selection), plus
  _inlineLinkBox() which renders a selectable input/textarea with all URLs when neither the share
  sheet nor the clipboard is available. No prompt() anywhere on this path.
C fullscreen: requestFullscreen targeted .fm-preview-body, which sits INSIDE the pane but excludes
  the toolbar, so ⛶ and ✗ disappeared and only the OS back gesture got out. Now fullscreens
  #filemgr-preview — toolbar, ✕ and ⛶ stay on screen and ⛶ toggles.
D webdav move: bulk Move asked for the destination with prompt(), which returns null in iOS
  standalone PWAs and most Android WebViews, so it silently did nothing and looked unimplemented.
  Destination is now an inline row in the bulk bar (44px input + "Move here"/"Cancel", prefilled).

Verified on the served code: ext bundle md5 5f440c77b6ab5529729aee8019a6c351 (served == local),
webdav.js carries wdav-move-dest x2, and a headless browser probe on the real page shows the toolbar
as ["✕","⛶","📋","🔗"], closing the preview prints "Preview closed — selection kept" with the
selection intact, selecting 3 files and copying yields a textarea with the 3 real WebDAV URLs, and
Download with nothing selected explains what to do. 6 PASS on the URL test, no-undef clean,
v4.6.99, help 362/362.

Not done, deliberately: cut/copy + paste across the VFS/WebDAV border. Recorded as Issue D2 in the
plan with the exact insertion points, the upload-then-delete ordering rule and the failure case.

0 files changed, 0 insertions, 0 deletions