docs: small reader-facing cleanups (ADO 5350804) (#522)

Two small reader-facing fixes bundled to avoid trivial-PR overhead:

- samples-mistral/README.md: fix empty [uv]() link target to
  https://docs.astral.sh/uv/, and add the standard sample frontmatter
  (page_type, languages: python, products, description).
- .azure-pipelines/README.md: add 'Last updated: 2026-06-10' line and a
  'See also' section cross-referencing docs/validation-contract.md,
  docs/validation-results-contract.md, and docs/repo-sync-automation.md.

The third cleanup proposed in the ADO Task (.infra/pytest_plugins/
changed_samples/README.md stub) is deferred — it should be folded into a
broader proposal to either fully document or fully remove the
pytest-changed-samples plugin + tox/conftest scaffolding, which exceeds this
Task's authority.

ADO 5350804: https://msdata.visualstudio.com/Vienna/_workitems/edit/5350804

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Author: 3 people

samples-mistral/README.md

@@ -1,13 +1,23 @@
+---
+page_type: sample
+languages:
+- python
+products:
+- azure-ai-foundry
+description: Python notebooks for Mistral AI models on Azure AI Foundry — Mistral Large, Document AI, and OCR with vision.
+---
+
 # Mistral AI models on Azure Foundry
 
 This subdirectory contains code samples to get started with Mistral AI models on
 the Azure Foundry platform.
 
 ## Getting started
 
-The recommended way to set up your environment is to leverage [uv](). Otherwise you
-can rely on the auto-generated `requirements.txt` file with the package manager of
-your choice (e.g. pip, poetry, etc.)
+The recommended way to set up your environment is to leverage
+[uv](https://docs.astral.sh/uv/). Otherwise you can rely on the auto-generated
+`requirements.txt` file with the package manager of your choice (e.g. pip,
+poetry, etc.)
 
 To install the required dependencies and start a notebook server, run the following
 commands in your terminal: