docs: update links to relocated PyPI documentation

[blackorange-mega]

PyPI's user documentation moved from warehouse.pypa.io/api-reference/ to docs.pypi.org, and pipx moved off pypa.github.io. Six links across three docs pages currently 404.

File	Old link	New link
docs/repositories.md (L335)	warehouse.pypa.io/api-reference/json.html	docs.pypi.org/api/json/
docs/repositories.md (L72, L433, L445)	warehouse.pypa.io/api-reference/legacy.html#upload-api	docs.pypi.org/api/upload/
docs/cli.md (L952)	warehouse.pypa.io/api-reference/xml-rpc.html#deprecated-methods	docs.pypi.org/api/#api-preference
docs/contributing.md (L241)	pypa.github.io/pipx/	pipx.pypa.io/stable/

Every replacement URL was checked and returns 200; the old ones return 404.

One case needed a judgement call. The XML-RPC page has no direct successor — that API was removed rather than relocated, and docs.pypi.org/api/ lists only the Index, JSON, BigQuery and Upload APIs. The deprecation notice the old #deprecated-methods anchor pointed at now lives in the API Preference section of the API index ("No new integrations should use the XML-RPC APIs as they are planned for deprecation"), so I pointed there. The surrounding note about PyPI search still reads correctly. If you would rather drop that link entirely, say the word.

Docs only; no code or behaviour changes.

[sourcery-ai]

Hey - I've found 1 issue

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path="docs/cli.md" line_range="952" />
<code_context>
 (via a browser) instead.

-For more information, please see [warehouse documentation](https://warehouse.pypa.io/api-reference/xml-rpc.html#deprecated-methods)
+For more information, please see [warehouse documentation](https://docs.pypi.org/api/#api-preference)
 and this [discussion](https://discuss.python.org/t/fastly-interfering-with-pypi-search/73597/6).
 {{% /note %}}
</code_context>
<issue_to_address>
**nitpick:** The link text still identifies the destination as “warehouse documentation,” but the replacement URL points to PyPI’s documentation site, misleading readers about where the guidance is hosted.

**Suggested fix:** Rename the link text to “PyPI API documentation” or similar.

```suggestion
For more information, please see [PyPI API documentation](https://docs.pypi.org/api/#api-preference)
```
</issue_to_address>

Sourcery assessment

Approved.

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[blackorange-mega]

Good catch — the link text said "warehouse documentation" while pointing at docs.pypi.org. Renamed it to "PyPI API documentation".

Checked the other labels I touched and left them alone, since they describe their destinations accurately: "JSON API" → docs.pypi.org/api/json/, "Upload API"/"Legacy Upload API" → docs.pypi.org/api/upload/. No "warehouse" wording remains in the three files.

[sourcery-ai]

Sourcery assessment

Approved.