fix: add distinct OnHold visual state to StatusBadge

[LockedTerminal]

Closes #450

• Add OnHold to InvoiceStatus enum in comebackhere-frontend types
• Add badge--on-hold CSS class to App.css (visually distinct from badge--pending via a solid amber border, same warm background tone)
• Add statusLabels map so OnHold renders as 'On Hold' (human-readable)
• Update aria-label to use the human-readable label
• Add StatusBadge.test.tsx covering all 7 status variants with explicit assertions for the new OnHold class, label text, aria-label, and that OnHold className differs from Pending

Checklist

• Closes #__
• Tests added or updated
• ABI snapshot updated if contract sources changed (abis/ and COMEBACKHERE-contracts/)
• Screenshots attached if UI changed
• Documentation updated if needed

Notes

• For contract changes, verify ABI snapshot hygiene with make check-abi-snapshots.
• For UI changes, include screenshots or screen recordings to help reviewers.

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