test: add languages testing for web app

[pikann]

Summary

• Add apps/web/src/i18n/locales.test.ts, a Vitest test that checks every locale under src/i18n/locales (en, vi, ko, zh-CN, ja, es, fr, ru, pt-BR) has the same namespace files and the same nested key structure as en, so a translation can never silently fall back due to a missing key.
• The test correctly ignores i18next's CLDR plural-suffix variance (e.g. Russian legitimately has _few/_many in addition to _one/_other) so real language differences don't trip a false positive.
• No CI workflow changes needed — web-pr-ci.yml already runs bun run test on every PR touching apps/web/**, so this test now runs automatically.
• Fixes a real gap the new test caught: home.stats.aiAgents.subActive existed only in en/shared.json and was missing from all 8 other locales, so non-English users silently saw the English string. Added the missing translation to each locale.

Test plan

• bun run test — full web suite green (locale test included)
• bun run lint
• bun run build

[pullfrog]

ℹ️ Solid, tight structural test — I verified locally that it actually fails when a key drifts. Two minor, deferrable suggestions below.

Reviewed changes

• Locale key-parity test — new apps/web/src/i18n/locales.test.ts mirrors the exact import.meta.glob("./locales/*/*.json") pattern and path regex config.ts uses, asserting each supported language's namespace files and key paths match en, with CLDR plural-suffix (_zero/_one/_two/_few/_many/_other) normalization.
• Missing aiAgents.subActive translations — adds the {{count}}-interpolated subActive copy to the 8 non-English shared.json files, fixing the home stats card (apps/web/src/routes/_authenticated/home/index.tsx:570) falling back to English for those locales.

ℹ️ Placeholder parity isn't asserted

The test pins key paths, but not the interpolation tokens inside the string values. A locale that drops or renames {{count}} still passes the path comparison while the UI renders a literal {{count}} configurados. Since collectKeyPaths already walks every leaf, comparing the {{...}} token set per leaf against the en equivalent would close that gap for near-free.

Technical details

# Placeholder parity

## Affected sites
- apps/web/src/i18n/locales.test.ts:70-74 — per-namespace key comparison covers paths only, not `{{...}}` tokens

## Required outcome
- A locale whose string leaf holds a different `{{...}}` token set than the `en` leaf fails the test.

## Suggested approach (optional)
- In the leaf comparison, also extract and compare `{{...}}` tokens (e.g. `value.match(/\{\{([^}]+)\}\}/g)`) per key path.

ℹ️ Nitpicks

• subActive in es, pt-BR (and fr's configurés) uses a single plural form, so a count of 1 renders as "1 configurados". Adding _one/_other variants is the idiomatic fix for those languages, and the test's plural-suffix stripping already tolerates them.

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