Add transcription language selection and fix app launch UX

[volodymyr-malishevskyi]

Summary

This PR adds language selection for transcription, so users dictating in
non-English can get accurate results. It also fixes two launch UX issues:
the dashboard was hidden on startup and the menu bar "Open Dashboard"
button could silently fail.

Problems & Solutions

1. Non-English dictation produced incorrect or mixed-language output

Problem: WhisperKit supports 98 languages and can auto-detect the
spoken language, but auto-detection is unreliable for short phrases or
accented speech. There was no way for users to lock the language.

Solution:

• Added a Transcription Language dropdown in Settings → General with
  all 98 Whisper-supported languages and an "Auto-detect" default.
• Added a compact language chip in the mini recorder overlay so users
  can switch language mid-session without opening Settings.
• The last 5 used languages appear at the top of both menus for fast
  re-selection.
• WhisperService.transcribe() now accepts a language parameter.
  Passing "auto" sends nil to WhisperKit, preserving the existing
  auto-detect behavior.

Note: Language selection only takes effect with multilingual models
(Large v3 Turbo, Medium). English-only (.en) models ignore it — a
hint is shown in Settings.

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2. The app started invisible — users had no window on launch

Problem: On first launch (and after quitting all windows), the app
ran as a background process (.accessory activation policy). The only
way to open the dashboard was to discover the menu bar icon, which is
not obvious to new users.

Solution:

• Removed the hardcoded .accessory policy on startup. macOS defaults
  to .regular, so SwiftUI's WindowGroup now opens the dashboard
  automatically.
• The Dock icon now appears reactively: it shows when any titled window
  is visible and hides when all windows are closed, using
  windowDidBecomeKey / windowWillClose observers in AppDelegate.

---

3. "Open Dashboard" in the menu bar could silently fail

Problem: Clicking "Open Dashboard" in the menu bar extra used
NSWorkspace.shared.open(URL(string: "speaktype://open")) — a URL-scheme
trick that relied on the app handling the URL. If the URL handler wasn't
registered or was slow, nothing happened.

Solution: Replaced with a direct SwiftUI openWindow(id: "main-dashboard")
call, followed by NSApp.activate() to bring the window to the front.

Notes

• AppStorage key for selected language: "transcriptionLanguage" (default "auto")
• AppStorage key for recents: "recentTranscriptionLanguages" (comma-separated, max 5)

Files changed

File	Change
speaktype/Services/WhisperService.swift	Added language param; maps "auto" → nil for WhisperKit
speaktype/Views/Screens/Settings/SettingsView.swift	Transcription Language section with 98-language dropdown
speaktype/Views/Overlays/MiniRecorderView.swift	Language chip with recent-languages menu
speaktype/Views/Screens/Dashboard/DashboardView.swift	Pass transcriptionLanguage to transcribe()
speaktype/Views/TranscribeAudioView.swift	Pass transcriptionLanguage to transcribe()
speaktype/App/AppDelegate.swift	Reactive dock policy via window observers; NSApp.activate() on launch
speaktype/App/speaktypeApp.swift	Replace URL hack with openWindow(id:)

[karansinghgit]

changes incorporated in PR #37

Thank you for your contributions!