fix: resolve sidebar CancellationError and truncate long toolbar version

[datlechin]

Summary

• Sidebar showed "Query execution failed: CancellationError()" on first Oracle connection due to a race condition between connection establishment and table loading
• Long database version strings (e.g., Oracle's full banner) overflowed the toolbar

Changes

• OracleConnection.swift: Re-throw CancellationError instead of wrapping it as an OracleError with a user-visible message
• SidebarViewModel.swift: Handle CancellationError silently (not a user-facing error); cancel previous load task before starting a new one
• ConnectionStatusView.swift: Add lineLimit(1), truncationMode(.middle), and frame(maxWidth: 280) to the version text. Full string shown in tooltip on hover.

Test plan

• Connect to Oracle 18c XE. Sidebar should not show CancellationError on first connect
• Oracle toolbar version truncates with "..." in the middle, full text in tooltip
• MySQL/PostgreSQL toolbar version unchanged (short enough to fit)
• Sidebar refresh still works