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-development/SKILL.md

@@ -0,0 +1,109 @@
+---
+name: python-development
+description: >
+  Coding standards, conventions, and patterns for developing Python code in the
+  Agent Framework repository. Use this when writing or modifying Python source
+  files in the python/ directory.
+---
+
+# Python Development Standards
+
+## File Header
+
+Every `.py` file must start with:
+
+```python
+# Copyright (c) Microsoft. All rights reserved.
+```
+
+## Type Annotations
+
+- Always specify return types and parameter types
+- Use `Type | None` instead of `Optional[Type]`
+- Use `from __future__ import annotations` to enable postponed evaluation
+- Use suffix `T` for TypeVar names: `ChatResponseT = TypeVar("ChatResponseT", bound=ChatResponse)`
+- Use `Mapping` instead of `MutableMapping` for read-only input parameters
+- Prefer `# type: ignore[...]` over unnecessary casts, or `isinstance` checks, when these are internally called and executed methods
+    But make sure the ignore is specific for both mypy and pyright so that we don't miss other mistakes
+
+## Function Parameters
+
+- Positional parameters: up to 3 fully expected parameters
+- Use keyword-only arguments (after `*`) for optional parameters
+- Provide string-based overrides to avoid requiring extra imports:
+
+```python
+def create_agent(name: str, tool_mode: Literal['auto', 'required', 'none'] | ChatToolMode) -> Agent:
+    if isinstance(tool_mode, str):
+        tool_mode = ChatToolMode(tool_mode)
+```
+
+- Avoid shadowing built-ins (use `next_handler` instead of `next`)
+- Avoid `**kwargs` unless needed for subclass extensibility; prefer named parameters
+
+## Docstrings
+
+Use Google-style docstrings for all public APIs:
+
+```python
+def equal(arg1: str, arg2: str) -> bool:
+    """Compares two strings and returns True if they are the same.
+
+    Args:
+        arg1: The first string to compare.
+        arg2: The second string to compare.
+
+    Returns:
+        True if the strings are the same, False otherwise.
+
+    Raises:
+        ValueError: If one of the strings is empty.
+    """
+```
+
+- Always document Agent Framework specific exceptions
+- Explicitly use `Keyword Args` when applicable
+- Only document standard Python exceptions when the condition is non-obvious
+
+## Import Structure
+
+```python
+# Core
+from agent_framework import ChatAgent, ChatMessage, tool
+
+# Components
+from agent_framework.observability import enable_instrumentation
+
+# Connectors (lazy-loaded)
+from agent_framework.openai import OpenAIChatClient
+from agent_framework.azure import AzureOpenAIChatClient
+```
+
+## Public API and Exports
+
+Define `__all__` in each module. Avoid `from module import *` in `__init__.py` files:
+
+```python
+__all__ = ["ChatAgent", "ChatMessage", "ChatResponse"]
+
+from ._agents import ChatAgent
+from ._types import ChatMessage, ChatResponse
+```
+
+## Performance Guidelines
+
+- Cache expensive computations (e.g., JSON schema generation)
+- Prefer `match/case` on `.type` attribute over `isinstance()` in hot paths
+- Avoid redundant serialization — compute once, reuse
+
+## Style
+
+- Line length: 120 characters
+- Format only files you changed, not the entire codebase
+- Prefer attributes over inheritance when parameters are mostly the same
+- Async by default — assume everything is asynchronous
+
+## Naming Conventions for Connectors
+
+- `_prepare_<object>_for_<purpose>` for methods that prepare data for external services
+- `_parse_<object>_from_<source>` for methods that process data from external services