fix(file-tree): give the whole row to the drop zone, and unwire the nested long-press

Two defects a Codex review found in the previous commit and in PR #648.

The folder's drop zone stopped at the action. Once the ⋯ became a sibling
of the header, `data-tree-drop-dir` and the drag handlers were still on
the header, and `resolveFileTreeDropZone` walks UP from whatever the
pointer hit — so dragging an entry over the ⋯ strip of a destination
folder found no zone on desktop, and on the web the dragover/drop
handlers never fired there either. The move just silently did nothing.
When a row has actions the wrapper IS the row now: it carries the drop
marker, `rowProps`, and the highlight, and the header keeps only what
belongs to the header. That also lets the drag source's `opacity-70` dim
the action along with the rest of the row. `rowProps` is typed against
HTMLElement because the row element is a button or a div depending on
whether the row has actions.

Long-press on a nested row opened the wrong menu. A folder's trigger
encloses its expanded descendants' triggers, and PR #648 spread
`useLongPressToOpenMenu` onto every one of them — so a single touch
pointerdown armed a timer per ancestor, and each fired its own
contextmenu from its OWN element. Long-pressing a file two levels deep
opened three menus, the outermost winning the screen. Radix's built-in
long-press survives nesting because all the triggers share one bubbling
event that the innermost preventDefaults; separate dispatches carry no
such interlock. The hook is unwired — which is what the PR description
said the tree does anyway — leaving the ⋯ button as the touch entry
point and Radix's own long-press underneath it. The hook and its tests
stay, now carrying the nesting warning.

Also corrected the asChild rationale in the two row comments: React
builds this DOM with appendChild, so the old wrapper span really did
contain the row div — the reason to merge onto the row is the inline
span's effect on the row's w-max/min-w-full sizing, not a parser split.

Geometry verified against the built CSS in headless Chrome: the drop
marker resolves from the ⋯ for both folder rows and spans the full
525.4px row; the ⋯ aligns at the same x on file and folder rows and
never overlaps a name, including the longest one.