feat(strategy): add Compound V3 (Comet) strategy facet

[jayeshy14]

Summary

Adds a compound*-prefixed strategy facet that supplies the vault's underlying asset to a Compound III (Comet) base market (cUSDCv3) and reports its position via Comet's rebasing balanceOf. Shape mirrors AaveStrategyFacet: Comet's balanceOf is a live-accruing rebasing balance, so the position needs no receipt-token bookkeeping and harvest is a no-op.

This gives the router a second deep-liquidity money market on Arbitrum (Aave ~$1.0B, Compound III among the top markets) with a different rate curve, so allocations diversify rather than duplicate Aave's risk profile.

What's included

• IComet — minimal interface (supply / withdraw / balanceOf / baseToken, plus the getUtilization / getSupplyRate view rate-readers a curator uses to price the market on-chain). Trimmed to the facet's surface, matching IAavePool.
• CompoundV3StrategyFacet — EIP-7201 slot vaultrouter.strategy.compound.
• MockComet + 23 unit tests (no RPC needed).
• CompoundV3Strategy.fork.t.sol — 4 tests against the live Arbitrum cUSDCv3 market, RPC-gated (auto-skips without ARBITRUM_RPC_URL).
• StorageNamespaces — pins the new namespace literal to its erc7201 hash.

Design decisions (where it diverges from the Aave facet)

1. Config validates comet.baseToken() == asset (the Morpho-style guard Aave lacks), so a market for the wrong asset can never be wired in.
2. Withdraw clamps to the position — Comet would tip an over-withdraw into a borrow, so compoundWithdraw clamps the request to balanceOf and measures the underlying actually received.
3. SUPPLY_ROUNDING_SLACK = 2 — Comet rounds principal down on supply, so a strict < amount check (like Aave's) would flake; a real fee-on-supply still trips the guard, and any reverting deposit becomes a per-strategy rebalance skip, not a bricked batch.
4. harvest is a no-op — base interest auto-accrues into balanceOf. COMP incentive rewards accrue separately via CometRewards (a non-underlying token needing its own claim/sell/account path) and are intentionally out of scope.

Testing

forge test                                  # 194 passed, 0 failed, 4 skipped (fork, RPC-gated)
forge test --match-contract CompoundV3StrategyTest
ARBITRUM_RPC_URL=<rpc> forge test --match-path test/integration/CompoundV3Strategy.fork.t.sol

Live Arbitrum addresses used by the fork test: Comet cUSDCv3 0x9c4ec768c28520B50860ea7a15bd7213a9fF58bf, base USDC 0xaf88d065e77c8cC2239327C5EDb3A432268e5831.

Notes

• Rebased onto main (which now contains the erc7201 slot conventions this work depends on); the diff is just the Compound facet.
• Known boundary (shared by every strategy): the Vault has no strategy pull-back hook yet, so redeems succeed only up to the idle reserve. Tests document this rather than paper over it.