test: add unit tests for useMultiSigProposals hook

[Horlarmmy]

Summary

Added unit test coverage for useMultiSigProposals hook, which manages multi-sig proposal state (creation, signing, cancellation, execution) via localStorage.

Changes

src/__tests__/hooks/useMultiSigProposals.test.tsx (new)

194 lines covering 12 test cases across 5 describe groups:

Group	Tests
Initial state	Empty localStorage → empty proposals; loads & filters by campaignId; re-filters on campaignId change
Error handling	Corrupted localStorage JSON → gracefully returns []
createProposal	Creates pending proposal & updates state immediately; no-ops when walletAddress is null; no-ops when active proposal exists; persists to localStorage
signProposal	Marks caller's signer entry as signed; transitions status to ready when threshold met; no-ops when walletAddress is null
cancelProposal / markExecuted	Sets status to cancelled; sets status to executed with txHash

Verification

Imports and patterns match existing hook tests (useCampaign.test.tsx). No changes were needed to the source hook — the hook already updates state synchronously inside createProposal, which satisfies the "refetch after submission" acceptance criterion.

Closes #803

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[sshdopey]

Auto-review failed (API error). Leaving PR for human review.