feat(connections): quick search and filter in database object tree (close #680)

[ZhuchkaTriplesix]

Summary

Closes #680.

Features Added

1. Global Sidebar Quick Search:

   • Quick search input in the connections panel with Ctrl+F / Cmd+F shortcut.
   • Case-insensitive filtering across connection names, database names, and hostnames.
   • Automatically expands folders containing matched connections.
   • Shows badge indicator for matched / total count (e.g. 1/3) and clear button.
   • Friendly empty state when no servers match query.

2. Inline Group Filter Bar (TreeObjectFilterBar):

   • Compact inline filter bar appears in expanded table/view/routine groups with $\ge 8$ items.
   • Real-time filtering with badge count (filtered/total).
   • Clean empty state with 'No matching tables/views' label.

3. Table & View Pinning:

   • Allows users to pin important tables and views to the top of the list.
   • Pinned items are marked with a gold star icon and always sort to the top.
   • Toggle pin via context menu or star action.

Tests

• test/features/connections/connection_tree_quick_search_test.dart added with unit and widget test coverage for search, auto-expanding folders, and pinned item sorting.
• Passed dart analyze with 0 issues.
• Passed flutter test test/features/connections/ with 50/50 tests passing.