feat: add autocompletion and multi-line for filter fields

[datlechin]

Summary

• Add native macOS autocompletion to filter text fields (Raw SQL and Value fields) — column names and SQL keywords suggested as user types
• Add multi-line support for Raw SQL filter field (Option+Enter for newline, Enter to apply)
• SQL keywords only suggested for SQL-based databases (SQL, CQL, PartiQL), not for MongoDB/Redis/etcd

Closes #521

Implementation

• CompletionTextField (NSViewRepresentable) wrapping CompletionNSTextField with custom NSTextFieldCell that provides a CompletionFieldEditor (NSTextView subclass)
• CompletionFieldEditor overrides completions(forPartialWordRange:indexOfSelectedItem:) for the native macOS completion popup
• Auto-triggers on typing via fieldEditor.complete(nil) in controlTextDidChange
• Follows existing CellTextField/CellTextFieldCell pattern in the codebase

Test plan

• Open filter panel on a SQL database table, select Raw SQL mode, type partial column name → native completion popup appears
• Select a column filter mode, type in Value field → column name suggestions appear
• Connect to MongoDB/Redis → verify only column names suggested (no SQL keywords)
• In Raw SQL mode, press Option+Enter → newline inserted; press Enter → filter applied
• Verify completion popup keyboard: ↑↓ navigate, Enter/Tab select, Escape dismiss
• Verify filter styling matches existing fields (size, font, border)