CYS3-02: Upgradeable Storage Layout Changes Can Corrupt Live Proxies

[evercoinx]

Note

Low Risk
Low risk: changes are limited to tests and documentation, mainly adding regression coverage for upgrade safety and stabilizing fork tests against oracle staleness.

Overview
Adds a new StorageLayout.t.sol regression test that pins storage layouts for all mainnet-deployed UUPS proxies (PolicyManager, ClaimManager, PremiumManager, SpecRegistry, Swapper, CoverPoolFactory) by comparing Foundry storageLayout output against a baseline (with AST-ID normalization).

Stabilizes Morpho fork tests by reducing COVERAGE_LIMIT, wiring ClaimManager with oraclePriceFeed + a 10% deviation tolerance in the fork setup, and introducing _skipFork() which advances time while mocking Chainlink latestRoundData() timestamps to avoid staleness reverts.

Updates AGENTS.md with explicit guidance on append-only state variable changes for deployed UUPS proxies and the requirement to update the pinned baselines alongside legitimate appends.

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