Source adapter authoring and qualification

Use the normative source adapter guide and `source-adapter.v1` schema. An adapter manifest declares identity, version, source kinds, configuration schema, credential locators, capability limits, privacy/network behavior, lifecycle support, checkpoint compatibility, and qualification maturity.

Adapters must implement bounded check and preview behavior before ingestion; redact secrets and sensitive samples; reject undeclared hosts and path escape; and bind checkpoints to adapter version, source schema, and plan digest. A declared capability is not a supported capability until qualification evidence passes. Publication must include versioned schemas, valid and invalid fixtures, security review, compatibility policy, and a release artifact digest.

The reference adapters and SDK live in `src/dataset/`. Addon skills only select and explain them; they must never duplicate adapter execution.