Add missing i18n keys for session sidebar and memory components

[yacosta738]

Context

Follow-up from #277 (session-memory-visibility). Components use i18n keys that haven't been added to the locales package yet.

Scope

Add locale keys to @corvus/locales for:

• session.history, session.justNow, session.minutesAgo, session.hoursAgo, session.daysAgo
• session.messageCount, session.sidebarLabel, session.expand, session.collapse, session.noHistory
• chat.newChat
• Dashboard memory component keys (memory.*)

Acceptance Criteria

• All i18n keys used by SessionSidebar.vue are defined in locales
• All i18n keys used by dashboard memory components are defined
• Both English and Spanish translations provided

[linear]

DALLAY-210