doc update sprint 3

[zyaoj]

What does this PR do? Please describe:

• correct data loader according to our examples
• add Jupyter notebook examples on data & data pipeline (add also nbsphinx)
• add to the tutorial a small note about the eos token (attention)
• fix typo in (basename “$CKPT_DIR”) (fix Quick start and Getting started documentation issue #964)
• add a small dpo training example in the end2end fine-tuning
• add setup w/ uv
• update logo to svg (can fix some lfs errors)

Does your PR introduce any breaking changes? If yes, please list them:
N/A

Check list:

• Was the content of this PR discussed and approved via a GitHub issue? (no need for typos or documentation improvements)
• Did you read the contributor guideline?
• Did you make sure that your PR does only one thing instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests?
• Did you verify new and existing tests pass locally with your changes?
• Did you update the CHANGELOG? (no need for typos, documentation, or minor internal changes)