Python: Fix prek runner duplication and add skills (#3791)

* Python: fix prek runner running fmt/lint in all packages on core change

When a core package file changed, run_tasks_in_changed_packages.py ran
fmt, lint, and pyright in ALL 22 packages (66 tasks). Only type-checking
tasks (pyright, mypy) need to propagate to all packages since type
changes in core affect downstream packages. File-local tasks (fmt, lint)
only need to run in packages with actual file changes.

This reduces a core-only change from 66 tasks to 24 tasks (2 local +
22 pyright).

Also adds no-commit-to-branch builtin hook to protect the main branch
from direct commits.

* Python: add agent skills extracted from AGENTS.md and coding standards

Add 5 skills to python/.github/skills/ following the Agent Skills format:
- python-development: coding standards, type annotations, docstrings, logging
- python-testing: test structure, fixtures, running tests, async mode
- python-code-quality: linting, formatting, type checking, prek hooks, CI
- python-package-management: monorepo structure, lazy loading, versioning
- python-samples: sample structure, PEP 723, documentation guidelines

* Python: deduplicate AGENTS.md and instructions with agent skills

* updated skills

* fixes from review

* Python: increase timeout for web search integration test

python/.github/skills/python-samples/SKILL.md

@@ -0,0 +1,77 @@
+---
+name: python-samples
+description: >
+  Guidelines for creating and modifying sample code in the Agent Framework
+  Python codebase. Use this when writing new samples or updating existing ones.
+---
+
+# Python Samples
+
+## File Structure
+
+Every sample file follows this order:
+
+1. PEP 723 inline script metadata (if external dependencies needed)
+2. Copyright header: `# Copyright (c) Microsoft. All rights reserved.`
+3. Required imports
+4. Module docstring: `"""This sample demonstrates..."""`
+5. Helper functions
+6. Main function(s) demonstrating functionality
+7. Entry point: `if __name__ == "__main__": asyncio.run(main())`
+
+## External Dependencies
+
+Use [PEP 723](https://peps.python.org/pep-0723/) inline script metadata for
+external packages not in the dev environment:
+
+```python
+# /// script
+# requires-python = ">=3.10"
+# dependencies = [
+#     "some-external-package",
+# ]
+# ///
+# Run with: uv run samples/path/to/script.py
+
+# Copyright (c) Microsoft. All rights reserved.
+```
+
+Do **not** add sample-only dependencies to the root `pyproject.toml` dev group.
+
+## Syntax Checking
+
+```bash
+# Check samples for syntax errors and missing imports
+uv run poe samples-syntax
+
+# Lint samples
+uv run poe samples-lint
+```
+
+## Documentation
+
+Samples should be over-documented:
+
+1. Include a README.md in each set of samples
+2. Add a summary docstring under imports explaining the purpose and key components
+3. Mark code sections with numbered comments:
+   ```python
+   # 1. Create the client instance.
+   ...
+   # 2. Create the agent with the client.
+   ...
+   ```
+4. Include expected output at the end of the file:
+   ```python
+   """
+   Sample output:
+   User:> Why is the sky blue?
+   Assistant:> The sky is blue due to Rayleigh scattering...
+   """
+   ```
+
+## Guidelines
+
+- **Incremental complexity** — start simple, build up (step1, step2, ...)
+- **Getting started naming**: `step<number>_<name>.py`
+- When modifying samples, update associated README files