fix(i18n): align all 14 locales + strict key parity (no dead keys, no dupes)

What & why

The 14 frontend locale files were fragmented — 90 keys diverged across locales (missing in some, extra in others), the root cause of the aiGeneratedNoDocs near-miss and the reason a strict parity test was never enforceable.

Audited every divergent key against actual code usage (literal $t()/translate() + dynamic bracket access):

Category	Count	Action
Dead (orphaned by removed features)	81	Removed from every locale that had them
Used but missing from some locales	9	Added with real translations

Dead clusters (verified 0 code refs, incl. dynamic): admin.userEdit.*, admin.reindex*/dbActions.reindex/operations.reindexDatabase, settings email-change + account-deletion, chatbot.streamTimeout/generating/translationFailed, quickhelp.* prompts.

EN was right on the admin/settings clusters (already clean); the dead keys lived in other locales. The fix is mostly deletion (−299 lines), not addition.

Also fixed a typo: sw responseRating.ratingLabels key 44 → 4 (value was correct; caught via dynamic-usage check — ratingLabels[rating] is used).

Result

All 14 locales now share an identical 1136-key set (deep parity, 0 drift).

Test (strict — replaces baseline tolerance)

localeConsistency.test.js now enforces, CI-blocking:

1. All 14 locales share the identical deep key set (any missing/extra key fails).
2. No duplicate keys within any file (AST scan — JS silently keeps the last value for a dup key, so this needs source-level detection). Removed localeParity.baseline.json (the tolerance hack is no longer needed).

Verification

• frontend: 1223 tests pass, ESLint clean, Prettier clean.
• Method: surgical line-deletion (formatting preserved) + by-hand translated insertions — no full reserialize.
• CI green before merge.