Limitcast 0.17.2: accurate doctor and memory checks

Fixes doctor failures for Claude sessions that have not received their first assistant response and for legitimately absent subscription rate-limit fields. Malformed readings still fail validation.

Memory checks now follow plain filename citations, exclude agent policy files, and identify files without local links as review candidates that may be tracked in an external catalog. The memory audit command checks external provenance before proposing repairs.

Validation: 201 tests passed; Biome checked 74 files.