fix(transcription): handle nullish params and normalize cloudTranscriptionMode in resolveStreamingFallbackTarget

[hsusul]

Fixes #1829

Problem

In src/helpers/transcriptionFallback.js:

1. resolveStreamingFallbackTarget threw TypeError: Cannot destructure property 'useLocalWhisper' of 'undefined' / 'null' when called without arguments or passed null/undefined.
2. cloudTranscriptionMode === "openwhispr" did not normalize casing or whitespace, treating "OpenWhispr" as non-cloud and returning "byok".

Solution

• Defaulted parameters with params || {} before destructuring.
• Normalized cloudTranscriptionMode with trim().toLowerCase().
• Added unit tests in test/helpers/transcriptionFallback.test.js.

Verification

• node --test test/helpers/transcriptionFallback.test.js (passes, 4/4 tests)
• npm run typecheck (passes, 0 errors)
• npm run lint (passes, 0 errors)
• npm run i18n:check (passes)
• npm run build:renderer (passes)
• git diff --check (clean)

[Chadpiha]

Thanks @hsusul — closing with #1829 (same convention as the #1840 note).

The only caller passes getSettings(), which is a Zustand state snapshot and can't be nullish. And cloudTranscriptionMode is written as a lowercase literal by every write site in the app's history, so old localStorage can't hold a mixed-case value either. The deciding factor on the normalization half: this value is compared case-sensitively in ~15 other places (audioManager, dictationStreamingRouting, the settings store's own deriveTranscriptionMode, …). Normalizing in just this one reader would make the fallback route disagree with the streaming session router for the same stored value — if mixed case ever became real, the fix would belong at the write/store boundary so all readers stay consistent.

Thanks for the continued energy! 🙏