a11y: Toolbar labels missing mnemonics and SetLabelFor associations

[Orinks]

Problem

Toolbar StaticText labels (Protocol, Host, Port, User, Password) have no & mnemonic characters and no SetLabelFor() calls. VoiceOver on macOS requires SetLabelFor for proper label association. The QuickConnect dialog correctly uses both — the toolbar should match.

File

src/portkeydrop/app.py:177-210

Fix

Add mnemonics (&Host:, P&ort:, etc.) and SetLabelFor() after each label-control pair.

[Orinks]

Closing as resolved by merged PR(s): #60.