i18n(mental-health): ship validated PHQ-9/GAD-7 translations and localize crisis copy

The PHQ-9/GAD-7 item wordings rendered in English for es/fr/it/pl users
(de was already validated). Replace them with the officially validated,
public-domain Pfizer/PRIME-MD localized screener wordings (distributed via
the MAPI Research Trust) rather than ad-hoc translations — re-wording a
validated instrument invalidates the score. Localize the crisis-resource
copy too: translate the descriptive parentheticals while keeping the org
proper-nouns (TelefonSeelsorge, Nummer gegen Kummer, krisenchat,
Find a Helpline) and the US brand lines (988, Crisis Text Line) verbatim.

Add the new mental-wellbeing module label/description and the nav label
across all six locales.

src/lib/mental-health/instruments.ts

@@ -6,7 +6,10 @@
  * for PHQ-9; Spitzer 2006 for GAD-7). This module owns the canonical NUMERIC
  * contract; the human wording lives in `messages/*.json` under
  * `mentalHealth.items.*` (officially-validated translations per locale, English
- * fallback otherwise — re-wording invalidates the score).
+ * fallback otherwise — re-wording invalidates the score). The de/es/fr/it/pl
+ * item wordings are the public-domain Pfizer/PRIME-MD validated localized
+ * versions distributed via the MAPI Research Trust (de: Löwe/Gräfe et al.); they
+ * are NOT machine-translated. See `.planning/research/v125/clinical-instruments.md`.
  *
  * PHQ-9 item 9 (index 8) is the passive self-harm ideation screen and is the
  * safety-critical field (see `crisis-resources.ts` + the API handler): any