fix(mcp): expose safe measurement reasons and provenance

[frahlg]

The public MCP profile could report missing household load without the reason or the energy evidence needed to explain it. measurement_diagnostics now provides five fixed read-only views: status, assets, energy, series catalogue and series. It retains Core's nulls, quality, reasons, interval metadata, Wh provenance, counts and source resolution. Charger/source/asset/metric names become grant-bound opaque selections. Unknown fields and text stay out; incomplete pages and failed reads return errors. The tool needs the existing owner-approved diagnostic grant and accepts no HTTP path, settings change, control or credential export.

diag_run and events_list no longer appear in discovery while Core does not serve them. Cached calls return an explicit service-side E_UNSUPPORTED result without reaching the box. Full technical API reads stay separate.

Fixes #42. Paired Core PR: srcfl/ftw#1746 (disabled charger warning and test fixture). CI runs the real Core handlers and temporary SQLite data from exact commit bf80760fb4d11698ca09e76f22ce44cf347b78df through OAuth, TLS, Noise and MCP. Missing/disabled EV sources retain their reason and association; an explicit repair restores live load while incomplete interval coverage stays unknown. Actual ledger provenance and stored series reach MCP without private identifiers.

Validation: full go vet ./..., go test -race ./..., dev-tag tests and import checks passed. Additional MCP race tests cover the paired Core path, grant refusal, HTTP failures, incomplete/malformed streams, private fields, unsafe arguments, unsupported operations and identifier separation. Core's full make verify and all 858 web tests passed.

Production Go growth: 337 net lines. This PR adds no new wire message, grant, release or deployment. It does not establish recovery in the reporting user's client or on physical equipment.

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-19T05:49:23.253747Z	027ccde	PR opened

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