Fix Chapter 1.3: migrate removed question-answering/summarization/translation pipelines to text-generation (Transformers v5)

[critesjosh]

What does this PR do?

The question-answering, summarization, and translation pipelines were removed in Transformers v5.3. As a result, three code samples in Chapter 1 §3 ("Transformers, what can they do?") now fail on current Transformers with:

KeyError: "Unknown task question-answering, available tasks are [...]"

(and the equivalent for summarization and translation). This affects both the course page and its auto-generated Colab notebook.

Fix

Following the official v5 migration guide — which recommends replacing these task pipelines with the text-generation pipeline and a chat model — this PR rewrites all three sections to prompt an instruction-tuned model:

• Question answering → now generative (via text-generation) instead of extractive; the surrounding prose is updated to reflect this.
• Summarization → text-generation with a summarize prompt.
• Translation → text-generation with a translate prompt.
• Added a short note in the pipelines overview explaining that these tasks no longer have dedicated pipelines as of v5.

All example outputs were captured from a real run on transformers==5.13.

Notes / decision points for reviewers

• Model choice: I used HuggingFaceTB/SmolLM2-360M-Instruct to stay consistent with the SmolLM2-360M model already used earlier in this chapter and to keep it light enough for free Colab. The migration guide's own example uses Qwen/Qwen3-4B-Instruct-2507, which produces higher-quality output at a heavier download/compute cost — happy to switch if you'd prefer that.
• Extractive vs. generative QA: I moved QA to the generative approach for consistency with the other two tasks and with the migration guide. If you'd rather keep it extractive, it can instead use AutoTokenizer + AutoModelForQuestionAnswering (the approach taken in docs(tasks): remove references to removed question-answering pipeline transformers#44787).
• Scope: only the English source chapters/en/chapter1/3.mdx is changed; the localized copies are left to the course's translation workflow.

Refs #1197, #1211

[HuggingFaceDocBuilderDev]

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