feat: add optional You.com research provider

[mouse-value-add]

Why this is useful

• AgentPack already has an opt-in provider hook for learning output, so a small You.com Research adapter fits the existing shape.
• It gives the learning pipeline a way to pull live, cited web context when a task touches external docs or maintainer guidance.

What changed

• Added scripts/youcom_research_provider.py, a small JSON-in/JSON-out provider command that calls You.com Research with YDC_API_KEY.
• It derives a concise prompt from the current learning report and returns optional summary, learning_topics, concepts, and next_practice fields.
• Documented the setup in docs/configuration.md.
• Added a focused test for the prompt builder.

Setup

• Set YDC_API_KEY.
• Point learning.provider_command at python3 scripts/youcom_research_provider.py.

Usage example

• agentpack learn --provider-command 'python3 scripts/youcom_research_provider.py' --json

Validation

• python3 -m pytest tests/test_youcom_research_provider.py tests/test_docs_links.py -q

Fallback behavior

• If the API key is missing or the You.com request fails, the command exits non-zero and AgentPack keeps its default offline flow unless the user explicitly wires it in.

Tracking

• [Integration] vishal2612200/agentpack — optional You.com Research provider youdotcom-oss/integration-tracking#38