feat: orderable collection tree, richer data tables, responsive response area

[testsmith-io]

Collection tree

• Add a unified child order (Folder.childOrder) so requests and folders can be freely interleaved by drag-and-drop, with drop lines before every item (including at the top, under the collection name).
• The run plan follows the same order, so execution matches the tree.
• reorderChild store action; RequestRow/FolderRow become drag sources while drop lines own positioning; nesting still works by dropping on a folder.

Data tables

• Resolve {{variables}} and faker/dynamic expressions inside cell values, fresh per row (collection and folder level).
• Include data-table column names in {{...}} autocomplete.
• Run an individual request against a chosen data row (row picker on the send bar; new optional dataRow on the send payload).
• Collection runs now honour folder-level data tables (each folder's requests iterate by its rows; hooks run once).

Autocomplete

• Faker completions in VarInput now match the body editor: staged faker -> namespace -> method, with a CodeMirror-style icon/detail layout and matching order; typing "{{$" or "{{f" surfaces them.

Response area

• Two-row, container-query-responsive response toolbar that never scrolls horizontally: tabs fold into "More", actions into "..." as the panel narrows, active tab always visible (new accessible OverflowMenu).
• Expandable per-request detail in the run window (tests, console, script errors, sent request, received response) - the data the report carries.

Misc

• Default UI language is English unless the user has picked one.

Adds unit tests for data-row resolution, folder/collection data-table expansion, and child-order-driven run planning. All 7 locale catalogs updated (parity maintained).