Feature: Schema search and filter #37

Summary

Add a search/filter bar to the sidebar that allows users to quickly find tables, views, and columns by name across all schemas and databases.

Motivation

Production databases often have hundreds or thousands of tables. Scrolling through the sidebar tree to find a specific table is slow and frustrating. A quick filter/search (like VS Code's Ctrl+P file finder) would make navigation instant.

Proposed Behavior

• Shortcut: / in the sidebar activates search mode
• Filter: As the user types, the sidebar tree filters to show only matching items
• Fuzzy matching: Support substring matching (e.g., "usr" matches "users", "user_roles")
• Scope: Search across table names, view names, and column names
• Navigation: Arrow keys to navigate filtered results, Enter to select/expand
• Escape: Clear filter and return to full tree view

Acceptance Criteria

• / activates sidebar filter input
• Real-time filtering as user types
• Substring matching on table/view/column names
• Filtered tree shows matching items with parent context
• Arrow keys navigate filtered results
• Enter selects and expands matched item
• Escape clears filter
• Empty filter shows full tree
• Unit tests for filter matching logic