fix: correct pluralization of call counts in usage UI

[maxnoller]

Summary

• Token counts in the dashboard and models pages were rendered with hardcoded calls regardless of count, producing copy like "1 calls this month" or "across 1 calls".
• Added a shared pluralize(n, word, plural?) utility to console/src/lib/format.ts and replaced all affected strings.
• Also converted the inline ternary in the Catalog panel subtitle (${models.length} model${...}) to use the new helper for consistency.

Changes

File	What changed
console/src/lib/format.ts	Added exported pluralize() helper
console/src/lib/format.test.ts	Unit tests for pluralize()
console/src/routes/dashboard.tsx	Fixed "across X calls" (daily + monthly) and "X calls this month" in top-models list
console/src/routes/models.tsx	Fixed "X calls" in catalog monthly usage, "X calls today" in daily activity panel, and catalog subtitle

Test plan

• Verify pluralize(1, 'call') → "1 call" and pluralize(2, 'call') → "2 calls" via vitest unit tests
• Manually check dashboard Usage rollup panel with a gateway that has exactly 1 API call recorded — should read "across 1 call" and "1 call this month"
• Confirm normal multi-call counts still read "2 calls", "10 calls", etc.