refactor(ui): migrate toolbars, panels and the self-made buttons to QueryaButton #1337

Part of #1331. Needs QueryaButton, the split / menu button and the metrics issue.

Scope (from the review)

• Toolbars to one size per row: ERD (erd_view.dart), SQL workspace (generic_sql_workspace.dart), results and charts, data-grid staging, table view, Redis / Mongo / extension toolbars: QueryaActionButton -> QueryaButton, QueryaActionMenu triggers -> QueryaMenuButton, Execute -> QueryaSplitButton.
• Private copies removed: _ActionButton (mongo_collections_view.dart, mongo_databases_view.dart), _SmallActionButton (mongo_documents_view.dart), _TreeIconButton (mongo_document_tree_view.dart, 20 x 20 -> 28 hit area), _ToolbarButton (data_grid_staging_toolbar.dart), TableEditModeButton, ThemePickerButton's trigger.
• Bare InkWell / IconButton as buttons: Mongo documents pagination (square ripple, no tooltip, colour-only disabled), error-banner close icons, Redis pagination, the four copies of the show-password eye (-> one QueryaPasswordField or an adornment of the search field's family).
• Tooltips: every icon-only control gets one with kQueryaTooltipWait; the 6 literal delays go.
• Icon sizes inside buttons come from the size; the 13 / 14 / 15 / 16 / 18 hand-set values go.

Acceptance

• No private *Button class and no InkWell / GestureDetector button in lib/features/.
• Each migrated toolbar has one control height (layout test from the gallery).
• No visible regression in the e2e and widget suites; keys of existing buttons are kept.