bidi streaming improvements

[Robbilie]

i am using the adk-python bidi streaming example and i noticed some stuff that can be improved.

• active switch between sse and live endpoint
• allowing text input for bidi streaming
• allow for "pausing" of audio and video input
• support transcription output

might have some overlap with this PR, i could integrate some of it if required:
#156

the screensharing PR would need the same changes as i did for audio and video:
#116

another very valuable PR that i relied on because artifacts are currently not properly integrated:
#380

im looking to add modalities as an option to the ui, not sure if someone needs that though

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