test: cover major frontend pages

[Mkalbani]

Summary

• Added page-level Jest coverage for locations, licenses, maintenance, and asset details.
• Covered tree rendering, renewal warnings, seat assignment, calendar switching, scheduling, core tabs, actions, and asset not-found state.
• Added shared Jest DOM matcher setup.

Validation

• 9 focused tests passing
• ESLint: 0 errors

Closes #1324
Closes #1325
Closes #1326
Closes #1327

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[yusuftomilola]

No merge conflicts with main. Good test coverage additions across the major frontend pages - approving.