feat: import auth files from Add Account dialog

[rexinshimin0001]

Summary

• Add an authenticated POST /api/accounts/import-auth endpoint for importing uploaded/pasted auth JSON files.
• Add UI controls in the Add Account dialog to upload one or multiple auth.json files, or paste JSON content directly.
• Reuse scan-dir token parsing logic for email/auth type detection, add duplicate checks, safe filenames, and per-file skipped reasons.
• Fix existing frontend build blockers: wrap adjacent AccountCard JSX nodes and move the Google Fonts @import before Tailwind directives.

Why

Currently users need server filesystem access to place auth files under accounts/ and then scan the directory. This is inconvenient for remote deployments where users only have web UI access. The new flow lets authenticated users import auth files directly from the browser while preserving the existing directory scan flow.

Validation

• docker compose up -d --build succeeds.
• Container starts healthy.
• /api/health returns OK.
• New auth import endpoint rejects empty input and reports invalid JSON in skipped.
• Built frontend contains the new upload/paste import UI strings.