docs: concepts and building_applications migration (#3534)

# What does this PR do?

- Migrates the remaining documentation sections to the new documentation format

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## Test Plan

- Partial migration

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docs/source/distributions/importing_as_library.md

@@ -1,34 +0,0 @@
-# Using Llama Stack as a Library
-
-## Setup Llama Stack without a Server
-If you are planning to use an external service for Inference (even Ollama or TGI counts as external), it is often easier to use Llama Stack as a library.
-This avoids the overhead of setting up a server.
-```bash
-# setup
-uv pip install llama-stack
-llama stack build --distro starter --image-type venv
-```
-
-```python
-from llama_stack.core.library_client import LlamaStackAsLibraryClient
-
-client = LlamaStackAsLibraryClient(
-    "starter",
-    # provider_data is optional, but if you need to pass in any provider specific data, you can do so here.
-    provider_data={"tavily_search_api_key": os.environ["TAVILY_SEARCH_API_KEY"]},
-)
-```
-
-This will parse your config and set up any inline implementations and remote clients needed for your implementation.
-
-Then, you can access the APIs like `models` and `inference` on the client and call their methods directly:
-
-```python
-response = client.models.list()
-```
-
-If you've created a [custom distribution](building_distro.md), you can also use the run.yaml configuration file directly:
-
-```python
-client = LlamaStackAsLibraryClient(config_path)
-```