docs(i18n): document language packs across user, dev, and marketing docs

README + USER-GUIDE describe the sidebar picker and current coverage
(home + shared chrome, per-tool bodies pending). DEVELOPER gains a
how-to for adding packs and keys with the parity-test guarantee.
TECHNICAL §10b records the in-house-JSON architecture and locks in the
no-gettext decision (also logged in DECISIONS). REQUIREMENTS reflects
the new interface surface and updated test count. COPY.md adds a
"Language claim" slot so landing/email work can pick it up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/DECISIONS.md

@@ -174,6 +174,7 @@ $49-79/bundle · $149 full suite (when 3+ exist).
 | Apr 28 (v1.6) | Fold conversation-history content into docs (deduplicator spec, lead bundle use cases, full GUI matrix, 04/06 examples, Streamlit-to-SaaS reasoning) | No new decisions; promote at-risk analysis from chat history per no-silent-drift rule. |
 | May 1 (v1.6) | Mark Format Standardizer **Ready** | 199-row buyer corpus passing; Tier 1 + most Tier 2 built. |
 | May 1 (v1.6) | Add `src/core/errors.py` structured hierarchy | Uniform helpful messages across CLI + GUI. See TECHNICAL §7. |
+| May 13 (v1.6) | Ship in-house JSON i18n + EN/ES packs | Expand addressable market (Spanish-first buyers, LatAm bookkeepers) without a `gettext` build step. JSON packs editable by non-devs; parity test prevents drift. See TECHNICAL §10b. |
 
 ## 8. Re-lock triggers