.NET: Python: Add AGENTS.md files and update coding standards (#3644)

* Add AGENTS.md files and update coding standards for Python

- Add root python/AGENTS.md with project structure and package links
- Add AGENTS.md for each package describing purpose and main classes
- Update .github/copilot-instructions.md with improved structure
- Update python/CODING_STANDARD.md with API review guidance:
  - Future annotations convention (#3578)
  - TypeVar naming convention (#3594)
  - Mapping vs MutableMapping (#3577)
  - Avoid shadowing built-ins (#3583)
  - Explicit exports (#3605)
  - Exception documentation guidelines (#3410)
- Simplify python/.github/instructions/python.instructions.md to reference AGENTS.md
- Remove AGENTS.md from .gitignore

* Fix purview import path in AGENTS.md

* Address PR review comments and restructure instructions

- Slim down .github/copilot-instructions.md to reference language-specific docs
- Add ADR section explaining templates and purpose
- Create dotnet/AGENTS.md with .NET-specific build commands, conventions, and sample guidance
- Update Python build/test instructions for core vs isolated changes
- Fix Microsoft.Extensions.AI package references
- Update kwargs guidance per issue #3642
- Fix Python sample helper placement (top, not bottom)
- Document new 'typing' poe task in DEV_SETUP.md

* Add 'typing' poe task to run both pyright and mypy

* Add kwargs guidelines from issue #3642 to CODING_STANDARD.md

* Clarify that connector packages pull in core as dependency

python/packages/ag-ui/AGENTS.md

@@ -0,0 +1,35 @@
+# AG-UI Package (agent-framework-ag-ui)
+
+AG-UI protocol integration for building agent UIs with the AG-UI standard.
+
+## Main Classes
+
+- **`AgentFrameworkAgent`** - Wraps agents for AG-UI compatibility
+- **`AGUIChatClient`** - Chat client that speaks AG-UI protocol
+- **`AGUIHttpService`** - HTTP service for AG-UI endpoints
+- **`AGUIEventConverter`** - Converts between Agent Framework and AG-UI events
+- **`add_agent_framework_fastapi_endpoint()`** - Add AG-UI endpoint to FastAPI app
+
+## Types
+
+- **`AGUIRequest`** / **`AGUIChatOptions`** - Request types
+- **`AgentState`** / **`RunMetadata`** - State management types
+- **`PredictStateConfig`** - Configuration for state prediction
+
+## Usage
+
+```python
+from agent_framework.ag_ui import add_agent_framework_fastapi_endpoint
+from fastapi import FastAPI
+
+app = FastAPI()
+add_agent_framework_fastapi_endpoint(app, agent)
+```
+
+## Import Path
+
+```python
+from agent_framework.ag_ui import AGUIChatClient, add_agent_framework_fastapi_endpoint
+# or directly:
+from agent_framework_ag_ui import AGUIChatClient
+```