S4: ai4x doctor — capability metadata validation

[normenmueller]

Parent Epic

#37

Scope

Implement capability metadata validation in the ai4x doctor CLI command. Doctor reads the central schema definition file and validates all .meta.yaml files under dev/cap/ against it. This is the first real implementation of the doctor command (currently a stub).

Scoped to metadata validation only — full doctor functionality is out of scope for this Epic.

Acceptance Criteria

AC-12 (Ubiquitous): The ai4x doctor command shall validate .meta.yaml files against the central schema definition file.

Note: AC-13 (schema change without code change) and AC-14 (missing schema error) also apply to doctor but are covered in S2 as shared constraints.

Dependencies

• S1: Define central capability metadata schema #38 (S1: schema file must exist)
• S3: Big-Bang metadata migration #40 (S3: migrated data for meaningful validation testing)

Not dependent on: #39 (S2). Doctor and CI scripts are independent consumers of the same schema.