fix: Add Claude Sonnet 5.5 and GPT 6.1 Sol DeepNews models

[emmy-devop]

Requested by @wagnercosta

🔴 Review tier: HIGH — human review required

• Release — merging publishes a new asknews release to PyPI.

What

• asknews_sdk/api/chat.py::DeepNewsModel: add claude-sonnet-5-5 and gpt-6.1-sol.
• asknews_sdk/dto/alert.py::DeepNewsModel (alert source/report params): add claude-sonnet-5-5, gpt-6.1-sol and claude-opus-5-5.
• asknews_sdk/dto/alert.py::AlertReportModel: fix a missing comma that merged gpt-5.6-terra and meta-llama/Meta-Llama-3.1-405B-Instruct into one invalid ID. Both are now accepted, as the API schema lists them.
• README: when to use search_news() versus get_deep_news() (requested by @freqai), with a mocked test that runs the example.

No default changed. No existing model ID or method removed.

What was dropped from this PR

Commit d4477ac ("Sync additive SDK contracts with production 0.32.3") is undone by e15f313. It added things nobody asked for:

• 24 more DeepNews model IDs in both catalogs.
• gpt-6-astra in the alert contracts.
• A new distribution.get_top_n_articles_for_domains() method (sync and async) and its DTOs.
• A frozen production-contract fixture and tests that pinned both catalogs to it.

Any of these can come back in its own PR if wanted.

How tested

• coverage run -m pytest: 128 passed (Python 3.13, frozen lockfile).
• ruff check asknews_sdk: passed.
• No live or paid API calls.

Merge

Squash-merge, so the release notes carry one fix: entry (this PR's title) instead of the three branch commits.