ui(theme): use editorBackground and semantic palette tokens in SQL previews and document tree #1644

Problem

In lib/features/workspace/destructive_query_dialog.dart and lib/features/workspace/dml_preview_dialog.dart, the code block containers for SQL preview hardcode dark/light hex colors:

color: isDark ? const material.Color(0xFF141416) : const material.Color(0xFFF4F4F6),
...
color: isDark ? const material.Color(0xFFE2E8F0) : const material.Color(0xFF1E293B),

This bypasses the active workbench theme. On themes like Solarized Light or Nord Dark, the SQL preview appears as an out-of-place grey box with hardcoded foregrounds.

Similarly, in lib/features/mongodb/mongo_document_tree_view.dart (_leafValueColor), data types are colored with raw hex values (0xFF22C55E, 0xFF3B82F6, 0xFFF97316, 0xFF06B6D4) instead of reading from context.semanticPalette.

Change

• Replace the hardcoded container colors in destructive_query_dialog.dart and dml_preview_dialog.dart with context.workbench.editorBackground (or cs.card) and cs.foreground.
• Map MongoDB leaf data type colors to tokens in context.semanticPalette.