Backlog: more prose providers (Harper / LanguageTool) + the verbspec OpenAPI surface

[bdelanghe]

Low-priority backlog captured from the #22 / #6 work so it isn't lost. None blocking; the in-house deterministic checks stay the default.

More prose providers (extend the seam from #23)

The provider seam supports Vale (AUDIT_VALE) and textlint (AUDIT_TEXTLINT), opt-in, behind the shared { level, msg } shape. The tool-landscape review flagged two more companions worth a provider each, same pattern:

• Harper — modern offline grammar/spell (Rust, LSP); the best grammar companion. Catches real language mistakes Vale/textlint miss.
• LanguageTool / LTeX+ — deep + multilingual grammar via self-hosted HTTP API. Heavier (Java); only if grammar depth / multilingual matters.

Both opt-in (AUDIT_HARPER=1 / AUDIT_LANGUAGETOOL=1), optional deps, in-house default unchanged.

verbspec OpenAPI surface

verbspec projects a verb to CLI / MCP / Anthropic / OpenAPI. We wired the first three (#18, #19). The OpenAPI projection (an audit/extract HTTP surface via toOpenApiOperation) is unbuilt — filing for visibility; build if an HTTP/service surface is ever wanted.

Standing TODO (from README Status)

• Real strings.json catalog (productionization) — the demo catalog.json is a photo-frame placeholder.