fix(session-ui): count timeline tool types

[Brendonovich]

Summary

• show each timeline tool type's count instead of one total count
• pluralize Skill and Agent summaries through the UI i18n plural API
• cover mixed, repeated, localized, and lifecycle tool groups

Before / After

Before	After

Validation

• bun typecheck in packages/ui, packages/session-ui, and packages/app
• bun typecheck:e2e in packages/app
• bun run test:components -- --workers=3 in packages/session-ui (125 passed)
• focused app Playwright regressions for locale projection, reducer projection, queue, context resize, and working state
• bun test src --only-failures in packages/ui (47 passed)
• repository pre-push typecheck (33 packages passed)

Issues

• Linear OCD-166
• Synced GitHub issue anomalyco/opencontrol#214