feat(ui): control metrics and tokens shared by buttons, dropdowns, search fields and tab strips #1333

Part of #1331. Implements the scale of the standard issue.

Problem

Heights are defined in four places that do not agree: QueryaIconButtonDensity (28 / 32), QueryaDropdownTokens (36 / compact 26), QueryaTabStrip (dense 4 px vs 8 px vertical padding), and shadcn ButtonSize (scale 1 / 0.75 of a padding that depends on theme density). A toolbar row therefore has no common height by construction.

Scope

• lib/core/ui/querya_control_tokens.dart (next to querya_tree_tokens.dart): QueryaControlSize with the values sm, md, lg and height, horizontalPadding, fontSize, iconSize, iconGap, radius, and scaled(context) through uiScale.
• QueryaIconButton: density becomes size: QueryaControlSize (dense / standard kept as deprecated aliases for sm / md).
• QueryaDropdown, QueryaSearchField, QueryaTabStrip, QueryaToolbarButton: take their height, radius and font from the tokens; dropdown compact 26 becomes sm 28.
• One QueryaControlSize.of(context) default for a toolbar subtree (QueryaControlScope), so a toolbar sets its size once and its children follow.

Acceptance

• No literal 26 / 28 / 32 / 36 control height remains in the kit's widgets.
• A row of QueryaIconButton, QueryaDropdown, QueryaSearchField and QueryaTabStrip of one size has one height (widget test).
• Heights follow uiScale and text scale without overflow.