fix: Windows dev script quoting and empty-email validation message

[winetree94]

Summary

Two fixes found while capturing design screenshots on Windows:

• Root pnpm run dev failed on Windows — the single quotes in --filter '@tinyrack/tinyauth-*' are not stripped by cmd.exe, so pnpm received a literally-quoted pattern and reported "No projects matched the filters". Switched to escaped double quotes, which work on all platforms.
• Submitting the login/register/forgot-password form with an empty email showed "Invalid email format" — misleading for an empty field. The email schemas now check non-emptiness first (validation.email.required, added to en/ko/ja locales) and only then validate the format.

Verification

• pnpm --filter "@tinyrack/tinyauth-*" ls matches all workspace packages under cmd.exe
• Verified in the running app: empty submit shows "Please enter your email address", not-an-email still shows "Invalid email format"
• pnpm build passes (includes frontend tsc typecheck)
• Frontend unit tests for login/register routes: 36 passed
• biome check clean on changed files