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/instructions/python.instructions.md

@@ -1,11 +1,6 @@
 ---
-applyTo: '**/agent-framework/python/**'
+applyTo: 'python/**'
 ---
 
-See [AGENTS.md](../../AGENTS.md) for project structure, commands, and conventions.
-
-Additional guidance:
-- Review existing tests and samples to understand coding style before creating new ones
-- When verifying logic, run only related tests, not the entire suite
-- Resolve all errors and warnings before running code
-- Use print statements for debugging, then remove them when done
+See [AGENTS.md](../../AGENTS.md) for project structure and package documentation.
+Detailed conventions are in the agent skills under `.github/skills/`.