PromptClip agent improvements

[ashish-spext]

Confirm this is a new feature request

• I've checked the current issues, and there's no record of this feature request

Describe the feature

1 - Better detection of content_type of prompt clip [1]
Here maybe we can test by improving the name of arg itself and description.

2 - Driving indexing parameters instead of hardcoding
For cases where user wants to change scene index prompt or give scene extraction config current design will fail.
Same goes for spoken index parameters.

What if we emit the message that video is not indexed instead of indexing in agent.
And then reasoning engine takes up the indexing either on defaults or asks users for configuration.
Also, currently we are taking up first available scene index we can make this dynamic by taking any of the available scene indexes.

[1] - #54 (comment)

Additional Context

No response