M5: provider toggle + ElevenLabs settings, Kokoro style emulation, DataFlowBadge, audio cache UI, render/replay refactor; draft demo story; ADR-031..036

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Mrituanjay Nath Jhayesterday

Co-Authored-By: Claude Sonnet 5.5 noreply@anthropic.com Entire-Checkpoint: 01M66A70201A2DX8FKX2ZTR3QD