chore(i18n): add coverage audit + migration inventory

Translation infrastructure (@mana/shared-i18n + svelte-i18n + 35
per-module locale files with ~3500 lines across de/en/it/fr/es) is fully
wired, but 65/78 modules still hardcode German in .svelte templates
rather than calling {$_('module.key')}.

Adds:
  - scripts/audit-i18n-coverage.mjs — scans lib/modules/**/*.svelte for
    hardcoded German keywords (Abbrechen, Speichern, Löschen, etc.) in
    files that don't import $_(). Reports per-module hit counts,
    bucket (FULL/PARTIAL/NONE), and whether the locale file exists.
    Supports --summary and --top N flags.
  - pnpm run audit:i18n-coverage  wires it into the audit:* family
    (reporting only, not a CI gate — existing debt would fail
    validate:all otherwise).
  - docs/optimizable/i18n-migration-inventory.md — priority list,
    per-module workflow, and prevention plan.

Top offenders: broadcast (26 hits), articles (24), events (23),
invoices (22), quiz (20), stretch (20), library (19), profile (17),
skilltree (15, PARTIAL), calendar (14, PARTIAL). Modules without a
locale file (broadcast/articles/events/invoices/…) need the locale
stubs scaffolded first.

Real string migration is per-site careful work (key naming, 5-language
parity, UI visual QA) and is left for per-module follow-up sessions.

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

package.json

@@ -32,6 +32,7 @@
 		"audit:coupling": "node scripts/audit-module-coupling.mjs",
 		"audit:complexity": "node scripts/audit-complexity.mjs",
 		"audit:map": "node scripts/build-complexity-map.mjs",
+		"audit:i18n-coverage": "node scripts/audit-i18n-coverage.mjs",
 		"generate:dockerfiles": "node scripts/generate-dockerfiles.mjs",
 		"setup:env": "node scripts/generate-env.mjs",
 		"setup:secrets": "node scripts/setup-secrets.mjs",