Title: Add property test for vault funding authorization

[Emmyt24]

Description
Implement a property test proving vault funding requires proper authorization from funder.

Requirements and context

• Must be secure, tested, and documented where applicable
• Should stay reviewable and fit the current monorepo structure

Suggested execution

• Create branch: add-property-test-for-vault-funding-authorization
• Keep changes scoped to the issue and reference the task IDs in the PR

Implement changes

• Generate random funder addresses
• Run at least 100 iterations and annotate Property 82
• Assert unauthorized funding attempts fail
• Verify authorized funding succeeds

Test and commit

• Run the most relevant tests for the touched service or UI surface
• Include authorization flow documentation
• Call out edge cases, assumptions, and any follow-up work

Example commit message

test: add vault funding authorization property

Guidelines

• Prefer small, reviewable PRs
• Keep naming and data contracts consistent with the spec docs
• Preserve responsive and accessible behavior for frontend work

[Godbrand0]

can you assign me this task: https://www.drips.network/wave/stellar/issues/888771a2-c9de-44d6-bf0c-b0b7cb91c395/apply