fix(governance): harden Fordham voting contracts

[POWERFULMOVES]

Hardens the Mode-A governance model against the unresolved correctness and anti-forgery findings from PMOVES.AI #2154.\n\nChanges:\n- validate quorum/pass bounds and require a real 2-of-N-or-stronger committee\n- require exact, distinct committee membership and reject duplicate proposal/roll ids\n- snapshot the eligibility roll per proposal and enforce close-week/finalization state\n- persist immutable finalized tallies and defensively clone attestations\n- require canonical safe-integer tally preimages and exact approver/signature identity binding\n- expand regression coverage for configuration, lifecycle, and forgery cases\n\nValidation:\n- focused contract suite: 4 suites, 115 tests passed\n- full integrations Jest suite: passed\n- npm run typecheck: passed\n- npm run lint: 0 errors; 48 pre-existing no-explicit-any warnings outside this patch\n- git diff --check: passed\n\nParent follow-up: POWERFULMOVES/PMOVES.AI#2154

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Reviewing files that changed from the base of the PR and between 0b978a1 and 234a65c.

📒 Files selected for processing (7)

• integrations/contracts/__tests__/equalweight-governor-model.test.ts
• integrations/contracts/__tests__/member-registry-model.test.ts
• integrations/contracts/__tests__/mode-a-tally.test.ts
• integrations/contracts/__tests__/tally-signer-ed25519.test.ts
• integrations/contracts/equalweight-governor-model.ts
• integrations/contracts/member-registry-model.ts
• integrations/contracts/tally-signer-ed25519.ts

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