feat(app): extract the agent slice into i18n, en+ru (CLEAN-38)

[maksymhryzodub-prog]

Implements CLEAN-38 (subtask of CLEAN-33): https://dreamvention.atlassian.net/browse/CLEAN-38

Third in the stack — main ← #30 ← #31 ← this. Targets feat/CLEAN-37-i18n-user-slice; nothing merges until the chain is complete.

Moves all copy out of the agent list, card, detail item and chat screen: the 28 strings the scan found, plus the ones it could not see — status labels and relative timestamps assembled in script.

Keys, not text

• Status meta returns status.running instead of "Running", keeping the raw value for the default branch: if the runtime reports a status we have no wording for, it still shows verbatim rather than a key path.
• Restart overlay returns titleKey / bodyKey per stage ("Stopping current pod…" → "Deploying new pod…" → …).
• Relative timestamps return a bucket plus its number ({key: 'relative_time.minutes', count: 5}), so the unit and word order live in the locale file — "5m ago" becomes "5 мин назад" without touching the component.
• agentChat drops its hardcoded 'Restart failed' the same way the auth providers did: a failure flag plus whatever the server actually said.

The running counter keeps the number's emphasis through an <i18n-t> slot rather than splitting the sentence into fragments around the markup.

Two infrastructure bits this slice forced

Russian plural rules. The free-slots counter is a genuine plural, and Russian needs three forms where English has two — vue-i18n's default rule would pick the wrong branch for most numbers. Added pluralRules.ru to the shared i18n config, taught the translator prompt the branch order, and ru came back correct:

нет свободных слотов | {count} слот свободен | {count} слота свободно | {count} слотов свободно

Narrowed the message guard I added yesterday. It rejected a bare | alongside @ — but | is the plural separator, a feature we now use, not a mistake. It flags only @ outside the intentional @:key linked form.

Verification

• nuxt typecheck and nuxt build clean; ru strings present in the built client chunks.
• i18n:check green across 5 slice/locale pairs.
• Re-scan finds nothing hardcoded left in the slice. Remaining across app: chat (15) and template (4) — CLEAN-39 and CLEAN-40.

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