Machine-readable error registry — every wire-reachable error_code with retryable, bilingual fix hints, docs_url and category

Public, zero-auth error registry — call this ONCE at startup to load a complete recovery policy, instead of discovering the error vocabulary one failure at a time. Returns every error_code any Apier surface can serialise (209 today; the closed ErrorCode enum), each with retryable (is an identical retry after a short backoff worth attempting?), fix_hint_en / fix_hint_nb (one-line imperative remediation in English and bokmål), docs_url (the code's anchor on /docs/errors) and category (one of the closed ErrorCategory buckets for coarse routing). SINGLE SOURCE OF TRUTH: the rows are the runtime error catalog — the SAME table errorResponse reads when it stamps those fields onto a live 4xx/5xx envelope — so a value looked up here always equals the value the envelope carries, and the /docs/errors page is generated from the same table. Sorted by code, deterministic for a given deploy: data_freshness / last_verified are pinned to the catalog's own change stamp, and the strong ETag honours If-None-Match → 304. Category A discovery surface: no API key, soft per-IP rate limit, Cache-Control: public, max-age=300. Complements POST /api/v1/explain, which expands the subset of codes that carry a full Compliance Explainer template into a bilingual explanation object.