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>

docs/optimizable/i18n-migration-inventory.md

@@ -0,0 +1,91 @@
+# i18n Migration Inventory
+
+**Status as of 2026-04-22.** Run `pnpm run audit:i18n-coverage` for current numbers.
+
+## The gap
+
+The unified Mana web app has `@mana/shared-i18n` + `svelte-i18n`
+**fully wired** — per-module translation files live under
+`apps/mana/apps/web/src/lib/i18n/locales/{module}/{de,en,it,fr,es}.json`
+for 35 modules, with ~3500 lines of German and matching English /
+Italian / French / Spanish. The infrastructure is done.
+
+What's missing is the **usage**: most module `.svelte` templates
+hardcode German strings like `"Abbrechen"`, `"+ Neues Mood"`,
+`"Keine Daten"` instead of calling `{$_('module.key')}`.
+
+Scanning `lib/modules/**/*.svelte`:
+
+- **FULL** (4 modules) — all files import `$_()` from svelte-i18n
+- **PARTIAL** (9 modules) — mixed usage
+- **NONE** (65 modules) — German hardcoded throughout
+
+## Why not auto-migrate?
+
+String migration is per-site careful work:
+- pick a key name (or reuse existing one from the locale file)
+- pick the German source text (may differ slightly from existing keys)
+- add key to all 5 language files (de/en/it/fr/es)
+- replace in template, test UI visually
+- tests covering copy may break
+
+It's not a mechanical codemod. Each module is a session of its own.
+
+## Priorities
+
+Rank by `keyword-hits × user-impact`. Run the audit for current numbers:
+
+```bash
+pnpm run audit:i18n-coverage --summary --top 20
+```
+
+Top offenders (2026-04-22 snapshot):
+
+| Rank | Module | Hits | Files | Locale? | Notes |
+|---|---|---|---|---|---|
+| 1 | broadcast | 26 | 10 | ✗ | Content broadcast compose + recipient UI |
+| 2 | articles | 24 | 16 | ✗ | Reader view, highlights, filter labels |
+| 3 | events | 23 | 12 | ✗ | RSVP, guest list, discovery |
+| 4 | invoices | 22 | 9 | ✗ | Business-critical: line items, payment states |
+| 5 | quiz | 20 | 3 | ✗ | Edit + play flows, question types |
+| 6 | stretch | 20 | 6 | ✗ | Session flows, reminders, routines |
+| 7 | library | 19 | 11 | ✗ | Book/media tracker: status, filtering |
+| 8 | profile | 17 | 4 | ✓ | Interview flow, context overview |
+| 9 | skilltree | 15 | 11 | ✓ | PARTIAL — modals done, ListView hardcoded |
+| 10 | calendar | 14 | 15 | ✓ | PARTIAL — EventForm done, ListView labels |
+
+**Already FULL:** `body`, `todo`, `times`, and the modules whose
+keyword count is zero (either trivially small templates or consistent
+use of `$_()`).
+
+## Recommended workflow per module
+
+1. **If no locale file exists** — run the skilltree/moodlit layout as
+   a template. Start with: `nav.*`, `common.{save,cancel,delete,confirm}`,
+   `list.{empty,count,newItem}`, `create.{title,save,namePlaceholder}`,
+   plus module-specific vocabulary.
+2. **Extract German strings** into `de.json` — keep them verbatim so
+   existing copy doesn't regress.
+3. **Translate to `en.json`** (required for sync across language
+   switch). Keep `it/fr/es.json` with English fallbacks if translator
+   not available.
+4. **Replace in templates** — `import { _ } from 'svelte-i18n'` at the
+   top, then `{$_('module.key')}` inline. For attributes:
+   `placeholder={$_('module.namePlaceholder')}`.
+5. **Update `i18n/index.ts`** — add the module to `registerLocale()` if
+   it isn't already listed (broadcast/articles/events/invoices/quiz/
+   stretch/library/wishes/guides/habits/dreams/firsts/companion/
+   ai-missions all need entries).
+6. **Re-run the audit** — `pnpm run audit:i18n-coverage --summary` —
+   expect the module to move from NONE → FULL.
+7. **Manual browser test** — the audit is pattern-based; visual QA
+   catches anything it missed.
+
+## Prevention (future work)
+
+The audit currently reports only — it doesn't fail CI. A future step
+could graduate it to a gate that:
+- blocks PRs that *add* hardcoded German to ListViews already migrated
+- continues to tolerate existing debt until it's cleared
+
+Until then: `audit:i18n-coverage` is the contract.