Fix OSS CI validation baseline

[mkrtc]

Summary

• add the missing root tsconfig.base.json used by package TypeScript configs
• add the missing scripts/check-i18n-coverage.ts script already referenced by validate:ci
• refresh bun.lock workspace metadata so bun install --frozen-lockfile succeeds in CI

Problem

A fresh OSS checkout could not complete the configured validation workflow:

• bun install --frozen-lockfile reported that the lockfile needed updates
• package typechecks extended ../../tsconfig.base.json, but that file was not present at the repository root
• bun run validate:ci referenced scripts/check-i18n-coverage.ts, but the script was missing

This meant the public validation workflow could fail before reaching the actual test suite.

Solution

This PR restores the baseline files expected by the existing scripts/configs:

• adds a shared TypeScript base config with the repository-wide compiler defaults
• adds a CI-safe i18n coverage checker for literal translation keys in t(...), i18n.t(...), and Trans i18nKey callsites
• updates the lockfile metadata to match the current workspace layout/version so frozen installs are reproducible

Related PRs

Related to #662 and #906. This PR keeps the scope limited to the validation baseline and includes the current bun.lock refresh required for the configured bun install --frozen-lockfile CI step.

Validation

• bun install --frozen-lockfile
• bun run validate:ci