Python: restructure: Python samples into progressive 01-05 layout (#3862)

* restructure: Python samples into progressive 01-05 layout

- 01-get-started/: 6 numbered steps (hello agent → hosting)
- 02-agents/: all agent concept samples (tools, middleware, providers, etc.)
- 03-workflows/: ALL existing workflow samples preserved as-is
- 04-hosting/: azure-functions, durabletask, a2a
- 05-end-to-end/: demos, evaluation, hosted agents
- Old files moved to _to_delete/ for review
- Added AGENTS.md with structure documentation
- autogen-migration/ and semantic-kernel-migration/ preserved at root

* fix: switch to AzureOpenAI Foundry, fix CI failures

- Switch all 01-get-started samples to AzureOpenAIResponsesClient with
  Azure AI Foundry project endpoint (AZURE_AI_PROJECT_ENDPOINT +
  AZURE_OPENAI_RESPONSES_DEPLOYMENT_NAME + AzureCliCredential)
- Add _to_delete/ and 05-end-to-end/ to pyrightconfig.samples.json excludes
- Fix test paths in packages/ that referenced old getting_started/ dirs:
  durabletask conftest + streaming test, azurefunctions conftest,
  devui conftest + capture_messages + openai_sdk_integration
- Fix workflow_as_agent_human_in_the_loop.py import (sibling import)
- Update hosting READMEs and tool comment paths
- Replace root README.md with new structure overview
- Update AGENTS.md to document Azure OpenAI Foundry as default provider

* cleanup: remove _to_delete folder, copy resource files to active dirs

All files in _to_delete/ were either:
- Exact duplicates of files in the new structure (240 files)
- Same file with only comment path updates (100 files)
- One import-fix diff (workflow_as_agent_human_in_the_loop.py)
- One superseded minimal_sample.py

Resource files (sample.pdf, countries.json, employees.pdf, weather.json)
copied to 02-agents/sample_assets/ and 02-agents/resources/ since active
samples reference them.

* fix: address PR review comments, centralize resources, remove root duplicates

- Fix type annotation in 04_memory.py (string union -> proper types)
- Fix old sample paths in observability files
- Fix grammar/spelling in observability samples
- Move sample_assets/ and resources/ to shared/ folder
- Remove 8 duplicate observability files from 02-agents root
- Update resource path references in multimodal_input and provider samples

* fix: update broken links from old getting_started paths to new structure

- Update relative paths in READMEs: getting_started/ → 01-get-started/,
  02-agents/, 03-workflows/, 04-hosting/, 05-end-to-end/
- Fix absolute GitHub URLs in package READMEs
- Fix broken link in ollama package README

* fix: convert absolute GitHub URLs to relative paths for link checker

Absolute URLs to python/samples/ on main branch 404 until PR merges.
Converted to relative paths that linkspector can verify locally.

* fix: update link for handoff sample moved to orchestrations/

* fix: update chatkit-integration README path from demos/ to 05-end-to-end/

* fix: update broken links in orchestrations README to match flat directory structure

python/samples/02-agents/background_responses.py

@@ -0,0 +1,139 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+import asyncio
+
+from agent_framework import Agent
+from agent_framework.openai import OpenAIResponsesClient
+
+"""Background Responses Sample.
+
+This sample demonstrates long-running agent operations using the OpenAI
+Responses API ``background`` option.  Two patterns are shown:
+
+1. **Non-streaming polling** – start a background run, then poll with the
+   ``continuation_token`` until the operation completes.
+2. **Streaming with resumption** – start a background streaming run, simulate
+   an interruption, and resume from the last ``continuation_token``.
+
+Prerequisites:
+  - Set the ``OPENAI_API_KEY`` environment variable.
+  - A model that benefits from background execution (e.g. ``o3``).
+"""
+
+
+# 1. Create the agent with an OpenAI Responses client.
+agent = Agent(
+    name="researcher",
+    instructions="You are a helpful research assistant. Be concise.",
+    client=OpenAIResponsesClient(model_id="o3"),
+)
+
+
+async def non_streaming_polling() -> None:
+    """Demonstrate non-streaming background run with polling."""
+    print("=== Non-Streaming Polling ===\n")
+
+    thread = agent.get_new_thread()
+
+    # 2. Start a background run — returns immediately.
+    response = await agent.run(
+        messages="Briefly explain the theory of relativity in two sentences.",
+        thread=thread,
+        options={"background": True},
+    )
+
+    print(f"Initial status: continuation_token={'set' if response.continuation_token else 'None'}")
+
+    # 3. Poll until the operation completes.
+    poll_count = 0
+    while response.continuation_token is not None:
+        poll_count += 1
+        await asyncio.sleep(2)
+        response = await agent.run(
+            thread=thread,
+            options={"continuation_token": response.continuation_token},
+        )
+        print(f"  Poll {poll_count}: continuation_token={'set' if response.continuation_token else 'None'}")
+
+    # 4. Done — print the final result.
+    print(f"\nResult ({poll_count} poll(s)):\n{response.text}\n")
+
+
+async def streaming_with_resumption() -> None:
+    """Demonstrate streaming background run with simulated interruption and resumption."""
+    print("=== Streaming with Resumption ===\n")
+
+    thread = agent.get_new_thread()
+
+    # 2. Start a streaming background run.
+    last_token = None
+    stream = agent.run(
+        messages="Briefly list three benefits of exercise.",
+        stream=True,
+        thread=thread,
+        options={"background": True},
+    )
+
+    # 3. Read some chunks, then simulate an interruption.
+    chunk_count = 0
+    print("First stream (before interruption):")
+    async for update in stream:
+        last_token = update.continuation_token
+        if update.text:
+            print(update.text, end="", flush=True)
+        chunk_count += 1
+        if chunk_count >= 3:
+            print("\n  [simulated interruption]")
+            break
+
+    # 4. Resume from the last continuation token.
+    if last_token is not None:
+        print("Resumed stream:")
+        stream = agent.run(
+            stream=True,
+            thread=thread,
+            options={"continuation_token": last_token},
+        )
+        async for update in stream:
+            if update.text:
+                print(update.text, end="", flush=True)
+
+    print("\n")
+
+
+async def main() -> None:
+    await non_streaming_polling()
+    await streaming_with_resumption()
+
+
+if __name__ == "__main__":
+    asyncio.run(main())
+
+"""
+Sample output:
+
+=== Non-Streaming Polling ===
+
+Initial status: continuation_token=set
+  Poll 1: continuation_token=set
+  Poll 2: continuation_token=None
+
+Result (2 poll(s)):
+The theory of relativity, developed by Albert Einstein, consists of special
+relativity (1905), which shows that the laws of physics are the same for all
+non-accelerating observers and that the speed of light is constant, and general
+relativity (1915), which describes gravity as the curvature of spacetime caused
+by mass and energy.
+
+=== Streaming with Resumption ===
+
+First stream (before interruption):
+Here are three
+  [simulated interruption]
+Resumed stream:
+key benefits of regular exercise:
+
+1. **Improved cardiovascular health** ...
+2. **Better mental health** ...
+3. **Stronger muscles and bones** ...
+"""