v0.5.16 — status/state read per-feature VERIFICATION.md

Per-feature verification state was being read from a single global file, so one feature's close-out leaked into another's status.

Fixed

• bin/flow-tools.cjs / lib/maintenance.cjs — status-report, state-update, and doctor's verify-integrity check all read a single global .spec-flow/VERIFICATION.md. With per-feature specs, that surfaced a prior feature's verified flag and live gaps as the active feature's status (e.g. wiki-core showed platform-foundation's leftover gaps). All three now read .spec-flow/specs/<feature>/VERIFICATION.md, matching the per-feature path task-baseline already used; status-report guards a null feature.

Regression test asserts a stale global file does not leak. Tests: 117.

Full changelog: see CHANGELOG.md