Further improvements to DocAgent and demo

[marklysze]

Why are these changes needed?

initiate_task and execute_rag_query needed docstrings for better LLM usage. Improved the demo notebook to provide more robust workflow.

Related issue number

N/A

Checks

• I've included any doc changes needed for https://docs.ag2.ai/. See https://docs.ag2.ai/docs/contributor-guide/documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ There is a different number of reports uploaded between BASE (9c79c45) and HEAD (1c7fc2a). Click for more details.

HEAD has 1279 uploads less than BASE

Flag	BASE (9c79c45)	HEAD (1c7fc2a)
3.13	88	0
ubuntu-latest	143	1
commsagent-discord	9	0
optional-deps	141	0
3.9	78	0
3.10	99	0
browser-use	6	0
macos-latest	108	0
commsagent-slack	9	0
commsagent-telegram	9	0
windows-latest	119	0
core-without-llm	14	1
3.11	66	1
3.12	39	0
jupyter-executor	9	0
retrievechat-pgvector	10	0
retrievechat	15	0
agent-eval	1	0
gpt-assistant-agent	3	0
retrievechat-qdrant	14	0
graph-rag-falkor-db	6	0
teachable	4	0
retrievechat-mongodb	10	0
twilio	9	0
anthropic	16	0
cerebras	14	0
websurfer	15	0
gemini	15	0
retrievechat-couchbase	3	0
llama-index-agent	3	0
lmm	4	0
groq	14	0
mistral	14	0
long-context	3	0
interop	13	0
together	14	0
crawl4ai	13	0
docs	6	0
interop-crewai	9	0
interop-langchain	9	0
interop-pydantic-ai	9	0
websockets	9	0
bedrock	14	0
ollama	14	0
cohere	15	0
swarm	13	0
reasoning	14	0
falkordb	2	0
core-llm	3	0
autobuild	1	0
deepseek	1	0
neo4j	2	0
integration	11	0

Files with missing lines	Coverage Δ
...ents/experimental/document_agent/document_agent.py	31.62% <ø> (ø)

... and 55 files with indirect coverage changes