fix(toolbar): show real keyboard shortcuts in button tooltips (#1694)

[datlechin]

Fixes #1694.

Problem

The "Switch Connection" toolbar button's tooltip read Switch Connection (⌘⌥C), but the real default shortcut is ⌃⌘C (Cmd+Control+C).

Root cause

The toolbar .help() tooltips in MainWindowToolbar+Buttons.swift are hardcoded shortcut strings. ConnectionToolbarButton hardcoded ⌘⌥C, which had drifted from the canonical binding in KeyboardShortcutModels.swift (.switchConnection = .character("c", command: true, control: true)). Every toolbar tooltip shares this flaw: it can drift, and it ignores user rebindings (these shortcuts are customizable). Several also used the wrong modifier order (⌘⇧ instead of the macOS-standard ⇧⌘).

Fix

Root-cause refactor rather than swapping one symbol:

• Add KeyboardSettings.shortcutHint(_:for:), which resolves the live shortcut (honoring user overrides) and renders it through the canonical BoundKey.displayString.
• Rewire all toolbar tooltips to derive from it, so they show the real shortcut and follow rebindings. Dashboard (no shortcut) stays a plain label.
• Collapse the three duplicate copies of this helper (MainStatusBarView, QueryEditorView, PaginationControlsView) to delegate to the shared method, removing the duplication that let the toolbar drift.

The reported tooltip now reads Switch Connection (⌃⌘C), and Preview/Results/Export/Import pick up the correct modifier order too.

Tests

New ShortcutHintTests in KeyboardShortcutTests: the default Switch Connection hint is Switch Connection (⌃⌘C), a user override updates the hint, and a cleared or unset shortcut shows the label only. All pass; existing keyboard suites unchanged.

Notes

• No docs change: the shortcut value is unchanged (only the displayed tooltip), and docs/features/keyboard-shortcuts.mdx already lists Cmd+Control+C.
• swiftlint --strict clean on the changed files.