fix(contracts): enforce terminal-state invariants in resolve_market and unlock_tokens, remove fee-admin key landmine

[vitalis200]

Body:

Summary

Fixes three related contract-safety issues in contracts/predict-iq:

closes #1186 — disputes::resolve_market (the admin override, called from lib.rs::resolve_market) had no guard against re-resolving an already-Resolved or Cancelled market. Per INVARIANTS.md §3, those states are terminal "at all times"; without the guard, an admin could call this path twice with different outcomes after bettors had already claimed under the first outcome, allowing overpayment against an unchanged total_staked/outcome_stakes.
closes #1192 — voting::unlock_tokens hard-required MarketStatus::Resolved, but a Disputed market can also terminate via community-voted cancel_market_vote → Cancelled. Voters who locked governance tokens through cast_vote's fallback path (used when the governance token doesn't support balance_at) had no way to recover them if the market was later cancelled instead of resolved.
closes #1195** — admin::set_fee_admin/get_fee_admin read and wrote ConfigKey::GuardianAccount — the same key set_guardian/get_guardian use — instead of the dedicated ConfigKey::FeeAdmin that the real, wired-up flow (fees::set_fee_admin/get_fee_admin) correctly uses. The functions were dead code with no callers, but calling them would have silently overwritten the guardian address that gates pause/unpause/emergency governance. Removed rather than repointed, since fees::set_fee_admin already implements this correctly and is the one exposed via lib.rs.
closes #1193

Changes

• modules/disputes.rs: resolve_market now rejects with ErrorCode::CannotChangeOutcome if market.status is Resolved or Cancelled, matching the identical guard already used in cancellation::cancel_market_admin and resolution::finalize_resolution.
• modules/voting.rs: unlock_tokens now accepts Resolved or Cancelled as valid terminal states.
• modules/admin.rs: removed the dead, miskeyed set_fee_admin/get_fee_admin functions.
• test.rs / modules/voting.rs / modules/admin.rs: added regression tests for all three fixes.

Test plan

• cd contracts/predict-iq && cargo test disputes
• cd contracts/predict-iq && cargo test voting
• cd contracts/predict-iq && cargo test admin
• cd contracts/predict-iq && cargo clippy --all-targets --all-features -- -D warnings
• cd contracts/predict-iq && cargo build --release

Note: these commands could not be run to completion in the dev environment used to prepare this PR — main currently has ~27 pre-existing compile errors in unrelated production code (e.g. a missing `CANCEL_OUTCOME_INDEX

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