feat(i18n): register Brazilian Portuguese as a locale

Add pt-BR to the locale list and everything that hangs off it: the
client loader, Intl and date-fns mapping, the reply-language footers of
the Coach and insights prompts (English body, pt-BR footer, the same
path Korean and Dutch take), the citation-coverage normative words, the
no-key fallback copy, the AUDIT-C standard-drink line, country labels,
period search, CSV yes/no cells and the Telegram bare-word aliases.

The locale enums in the extract, managed-profile and record-settings
schemas now derive from the locale list instead of repeating it, and
the five notification and login-alert routes share one isLocale guard
instead of hand-rolled chains, so a later locale is one edit there.
A language tag is matched exactly and case-insensitively before its
primary subtag, so pt-BR and pt-PT browsers land on the Portuguese
bundle rather than English, and AUDIT-C no longer cuts a region tag to
two letters.

PHQ-9, GAD-7 and WHO-5 are not marked validated for pt-BR: the wording
has not been read against the published Brazilian forms, so readers get
the English items plus the existing note.

CONTRIBUTING.md

@@ -121,7 +121,7 @@ Contributors: branch off `main`; PRs target `main`.
 
 ## Translations
 
-HealthLog ships with English (`en`) and German (`de`) maintained by the project, plus French (`fr`), Spanish (`es`), Italian (`it`), Polish (`pl`), Korean (`ko`), and Dutch (`nl`) that are **AI-initial, community-maintained**. The maintained locales are reviewed line-by-line; the community-maintained ones surface a small banner inviting users to improve them.
+HealthLog ships with English (`en`) and German (`de`) maintained by the project, plus French (`fr`), Spanish (`es`), Italian (`it`), Polish (`pl`), Korean (`ko`), Dutch (`nl`), and Brazilian Portuguese (`pt-BR`) that are **AI-initial, community-maintained**. The maintained locales are reviewed line-by-line; the community-maintained ones surface a small banner inviting users to improve them.
 
 ### Improving an existing locale
 
@@ -136,7 +136,7 @@ To suggest a fix or improvement:
 
 ### Adding a new locale
 
-If you want to introduce a locale that isn't shipped (e.g. `pt-BR`, `cs`):
+If you want to introduce a locale that isn't shipped (e.g. `sv`, `cs`):
 
 1. Open an issue first using the **Translation request** template. We'll confirm the locale is in scope and decide whether it joins the AI-initial-community-maintained tier or the maintained tier.
 2. Copy `messages/en.json` to `messages/<locale>.json`.