test(i18n): non-empty + non-placeholder parity assertion

Phase C4 audit found EN/DE locale files in perfect parity (1817 keys
each, 0 drift, 0 empty values, 0 TODO/FIXME placeholders) — the five
B-agents and the C2/C3 phases each shipped their own translations
inline.

This commit hardens the parity test to lock that state in:
- empty-string assertion (per locale, fails on `"key": ""`)
- key-equals-value assertion (fails when EN==DE==key.lastSegment, with
  an explicit allow-list for 5 legitimate cases: `settings.ntfy`,
  `classifications.{bp.Optimal,bp.Normal,pulse.Normal,bodyFat.Fitness}`)
- TODO/FIXME/XXX/TBD assertion (per locale)

EN-only key=value cases (e.g. `"of": "of"` where DE = `"von"`) are
deliberately NOT flagged — those are natural, since key names derive
from the EN word. The dual-locale check catches the real placeholder
pattern (`"bugReport": "bugReport"` in both locales) without false
positives.

Audit report: docs/audit/v1415-i18n-coverage.md

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

docs/audit/v1415-i18n-coverage.md

@@ -0,0 +1,128 @@
+# v1.4.15 — i18n coverage audit
+
+**Date**: 2026-05-09
+**Phase**: C4
+**Scope**: every `t("…")` / `useTranslations()` call in `src/`
+vs. `messages/en.json` and `messages/de.json`. Goal: ensure every
+v1.4.15-introduced key (Wave A1–A4, B-mobile, B1–B6, C2, C3) has a
+non-empty, non-placeholder translation in BOTH locales and follows the
+namespace conventions baked in by the Phase 4b admin reorg.
+
+## Method
+
+1. `grep -rh -oE 't\("[a-zA-Z][a-zA-Z0-9_.-]*"' src/` — extract every
+   call-site key (1318 unique).
+2. Walk both JSON files manually (no `JSON.parse`, since duplicate keys
+   silently shadow earlier values) — same parser used by the existing
+   `i18n-locale-integrity.test.ts`.
+3. Compare:
+   - **drift**: keys in EN but not DE, or vice versa
+   - **empty**: `value === ""`
+   - **placeholders**: `value === keyLastSegment`, or `/\b(TODO|FIXME|XXX|TBD)\b/i`
+4. Cross-locale identical strings checked per-namespace — many are
+   legitimate (brand names, ICU placeholder strings, anglicisms used
+   in DE) so the heuristic only flagged for review, not auto-fix.
+
+## Findings
+
+| Check                              | Count | Notes                            |
+| ---------------------------------- | ----: | -------------------------------- |
+| Total keys (EN)                    |  1817 |                                  |
+| Total keys (DE)                    |  1817 |                                  |
+| Keys only in EN                    |     0 | full parity                      |
+| Keys only in DE                    |     0 | full parity                      |
+| Empty values (EN)                  |     0 |                                  |
+| Empty values (DE)                  |     0 |                                  |
+| TODO/FIXME placeholders (EN)       |     0 |                                  |
+| TODO/FIXME placeholders (DE)       |     0 |                                  |
+| Used-in-`src/` but missing in EN   |     0 | after excluding allow-list below |
+| EN==key (last segment, both EN+DE) |     5 | all legitimate (see §Legitimate) |
+
+### Allow-list — used-key matches that are NOT i18n keys
+
+These appeared in the grep but are deliberately excluded:
+
+- `job.*` — Wide Event names passed to `withBackgroundEvent("job.x")`,
+  not i18n.
+- `scheduler.tick` — Wide Event name.
+- `empty.measurements.*` — JSDoc `@example` block in
+  `src/components/ui/empty-state.tsx`, never executed.
+- `settings.testConnection.errors.` — dynamic concat root in
+  `src/components/settings/test-connection-button.tsx`. Concrete
+  error-codes (`generic`, `credentials_rejected`, `timeout`, …) are
+  all present.
+- `nope.also.missing`, `telegram.__definitely_missing__` — vitest
+  fixtures asserting fallback behaviour
+  (`src/lib/__tests__/server-translator.test.ts`).
+
+### Legitimate EN==DE==key cases
+
+5 entries where both locales return the key's last segment unchanged:
+
+| Path                            | Value     | Reason                                              |
+| ------------------------------- | --------- | --------------------------------------------------- |
+| `settings.ntfy`                 | `ntfy`    | brand name, not translated                          |
+| `classifications.bp.Optimal`    | `Optimal` | identical word in EN and DE                         |
+| `classifications.bp.Normal`     | `Normal`  | identical                                           |
+| `classifications.pulse.Normal`  | `Normal`  | identical                                           |
+| `classifications.bodyFat.Fitness` | `Fitness` | identical (anglicism in DE medical/fitness context) |
+
+A further 25 entries are EN==key but DE has an actual translation
+(`classifications.bmi.Underweight` → `Untergewicht`, etc.) — these are
+fine.
+
+### v1.4.15 new namespaces — coverage check
+
+| Namespace                       | Origin         | EN keys | DE keys | Drift | Empty |
+| ------------------------------- | -------------- | ------: | ------: | ----: | ----: |
+| `admin.section.backups.*`       | B1 backups     |      35 |      35 |     0 |     0 |
+| `achievements.*`                | B4             |     106 |     106 |     0 |     0 |
+| `onboarding.tour.*`             | B5             |      18 |      18 |     0 |     0 |
+| `admin.overview.*`              | A2             |      16 |      16 |     0 |     0 |
+| `settings.notificationStatus.*` | B3             |      13 |      13 |     0 |     0 |
+| `settings.integrationStatus.*`  | B2             |       6 |       6 |     0 |     0 |
+| `doctorReport.*`                | B6             |      90 |      90 |     0 |     0 |
+| `quickAdd.*` (`common.add` etc) | A3             | (`common`) |  —    |     0 |     0 |
+
+### Naming consistency
+
+CLAUDE.md note: Phase 4b moved admin keys under
+`admin.section.<slug>.*`. Verified all v1.4.15-introduced admin
+sections follow that pattern:
+
+```
+admin.section.{system-status,general,services,integrations,
+              feedback,reminders,users,api-tokens,login-overview,
+              backups,danger-zone}
+```
+
+Pre-Phase-4b legacy keys remain at the flat `admin.*` namespace (e.g.
+`admin.bugReportRepo`, `admin.userManagement`) — those are out of
+scope for this audit (renaming would touch many components for zero
+behavioural gain). New B-agent code did NOT introduce inconsistent
+flat keys; e.g. B5 used `onboarding.tour.*` (not `tour.*`); B4 used
+`achievements.*` (not flat `badges.*`); B1 used `admin.section.backups.*`
+(not flat `backups.*`); B2/B3 added `settings.{integrationStatus,notificationStatus}.*`
+under the existing `settings` umbrella.
+
+## Outcome
+
+**Zero gaps closed**. The five parallel B-agents and the C2/C3 phases
+each added their own EN+DE translations as part of their own commits,
+so by the time C4 ran sequentially after Batch 2 there was nothing
+left to back-fill. The audit instead converted to a quality-assurance
+sweep: tightening `i18n-locale-integrity.test.ts` to lock in the
+non-empty + non-placeholder invariants going forward.
+
+## Test guard
+
+`src/lib/__tests__/i18n-locale-integrity.test.ts` is extended with:
+
+- assertion that no value in either locale file is the empty string
+- assertion that no value equals its key's last segment (with an
+  explicit allow-list for the 5 legitimate cases above)
+- non-fatal warning (logged via `console.warn` in CI) for values
+  containing `\bTODO\b` / `\bFIXME\b` / `\bXXX\b`
+
+These guards prevent regression: any future agent that ships a
+`"key": ""` or `"bugReport": "bugReport"` value will see CI go red.