fix(web): explicitly resume AudioContext and play audio on first TTS load

[ki3nd]

AudioPlayer.playAudio() on first call went directly to loadAudio() without calling audio.play(), relying solely on autoplay=true. When audio is routed through AudioContext via createMediaElementSource, autoplay is unreliable and the AudioContext may be suspended, producing no sound despite a valid API response.

Mirror the SSE path (playAudioWithAudio) by explicitly resuming the AudioContext and calling audio.play() before streaming begins.

Fixes #35880

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods