Guard against invalid nucleotide characters in sequence

[fabgpt-coder]

FabGPT — code quality

File: src/decks/community/TurboGenome/TurboGenomeEngine.ts

Rationale: The nucleoToFreq method returns a default frequency of 100 for any character that is not a valid nucleotide (A, C, G, T). If the sequenceStr contains invalid characters (e.g., 'N' for unknown bases or user input errors), the engine will generate an unintended sound instead of handling the error gracefully. Adding a validation check ensures the engine only processes valid biological sequences or skips invalid characters, preventing silent data corruption in the audio output.

Proposed by FabGPT OS and approved by a human before opening.

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🤖 FabGPT OS · source quality · model qwen/qwen3.5-9b · task f7372e2b3041d197 · HITL-approved before opening.

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