docs: add Python filters README with samples guide

Author: lawcontinue

python/samples/concepts/filtering/README.md

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+# Filtering Samples
+
+This directory contains samples demonstrating the Python filter system in Semantic Kernel.
+
+Filters allow you to intercept and modify pipeline execution at specific points. The Python SDK supports three filter types.
+
+## Filter Types
+
+| Filter | Decorator | Purpose |
+|--------|-----------|---------|
+| **Prompt Rendering** | `@kernel.filter(FilterTypes.PROMPT_RENDERING)` | Intercept before/after prompt is rendered |
+| **Function Invocation** | `@kernel.filter(FilterTypes.FUNCTION_INVOCATION)` | Intercept before/after any function call |
+| **Auto Function Invoke** | `@kernel.filter(FilterTypes.AUTO_FUNCTION_INVOCATION)` | Control automatic tool calls |
+
+## Samples
+
+### [prompt_filters.py](./prompt_filters.py)
+
+Basic prompt rendering filter. Demonstrates how to inspect and modify prompts before they're sent to the model.
+
+### [function_invocation_filters.py](./function_invocation_filters.py)
+
+Function invocation filter with logging and exception handling. Shows both `kernel.add_filter()` and `@kernel.filter()` decorator registration.
+
+### [function_invocation_filters_stream.py](./function_invocation_filters_stream.py)
+
+Same as above but for **streaming** responses. Use this when working with streaming chat completions.
+
+### [auto_function_invoke_filters.py](./auto_function_invoke_filters.py)
+
+Controls which automatic tool calls are allowed. Demonstrates `context.terminate = True` to skip specific function calls, and `FunctionResultContent` handling.
+
+### [retry_with_filters.py](./retry_with_filters.py)
+
+Implements automatic retry logic using function invocation filters. Retries on failure with a different model.
+
+### [retry_with_different_model.py](./retry_with_different_model.py)
+
+Similar retry pattern but specifically switches to a fallback model on failure.
+
+## Registration
+
+There are two ways to register a filter:
+
+```python
+# Method 1: Decorator
+@kernel.filter(filter_type=FilterTypes.FUNCTION_INVOCATION)
+async def my_filter(context, next):
+    await next(context)
+
+# Method 2: Add function
+kernel.add_filter("function_invocation", my_filter)
+```
+
+Both are equivalent. Use whichever fits your code style.
+
+## Filter Signature
+
+All filters follow the same signature:
+
+```python
+async def filter_name(context: <ContextType>, next: Callable) -> None:
+    # Code before next filter/function runs
+    await next(context)
+    # Code after next filter/function runs
+```
+
+The `next` callable passes control to the next filter in the chain, then to the actual function. You can skip execution by not calling `await next(context)`.
+
+## Terminating Auto Function Calls
+
+To prevent an auto-invoked function from executing:
+
+```python
+@kernel.filter(FilterTypes.AUTO_FUNCTION_INVOCATION)
+async def selective_filter(context: AutoFunctionInvocationContext, next):
+    if context.function.name == "dangerous_function":
+        context.terminate = True  # Skip this function call
+        return
+    await next(context)
+```