feat(applications): add shorcut for application modal

[DonnaIsabel97]

Summary

Adds the keyboard shortcut requested in #7. On the Applications page, pressing n now opens the Add application modal when the user is not typing in a form field.

Changes

• Added a guarded keydown listener on the Applications page.
• Pressing n opens the Add application modal.
• Prevented the n key from being inserted into the Role title field when the modal opens.
• Ignored the shortcut when focus is inside an input, textarea, select, or editable element.
• Preserved existing modal behavior, including closing with Esc.

Checklist

• Tests added or updated
• ruff, mypy, and pytest pass for the backend
• npm run lint, npm run typecheck, npm test, and npm run build pass for the frontend (if touched)
• Documentation updated where relevant
• No secrets, debug output, or commented-out code left behind

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