feat(ci): wire contracts/*.sol into hardhat, bump solc to 0.8.26 cancun

PR #27 unbroke `npx hardhat compile` (got `npm ci` working), but the job
still output "Nothing to compile" — hardhat looked at `deploy/contracts/`
which doesn't exist; the repo's Solidity sources live in `contracts/` at
the repo root.

This wires them up properly:

- `paths.root = ".."` + `paths.sources = "contracts"` points hardhat at
  the real source tree. `paths.tests` / `paths.cache` / `paths.artifacts`
  follow the same root-relative convention so the structure stays clean.
- Solidity bumped to `0.8.26` with `evmVersion: "cancun"` because
  `@openzeppelin/contracts ^5.0.0` (already in `package.json`) uses
  `mcopy` in `utils/Memory.sol`, which needs the cancun opcode.

Verification (locally, from `deploy/`):

```
$ rm -rf cache artifacts && npx hardhat compile
Compiled 24 Solidity files successfully (evm target: cancun).
```

The `contracts` CI job on main will now actually type-check the four
Solidity files we ship — `MeridianVault.sol`, `MeridianVaultERC4626.sol`
(ERC-4626 vault-share token), `OracleAdapter.sol`, `StrategyExecutor.sol`
— instead of silently succeeding on an empty source set.

Follow-up (separate PR): fix the `_getChainlinkPrice(pairId, ...)` vs
`pairId(string)` name-shadowing warning in OracleAdapter.sol.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: abhicris

.github/workflows/ci.yml

@@ -13,13 +13,10 @@ jobs:
 
   contracts:
     runs-on: ubuntu-latest
-    defaults:
-      run:
-        working-directory: deploy
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
           node-version: '20'
       - run: npm ci
-      - run: npx hardhat compile
+      - run: npm run compile

deploy/hardhat.config.js

@@ -2,8 +2,18 @@ require("@nomicfoundation/hardhat-toolbox");
 
 module.exports = {
   solidity: {
-    version: "0.8.24",
-    settings: { optimizer: { enabled: true, runs: 200 } },
+    version: "0.8.26",
+    settings: {
+      optimizer: { enabled: true, runs: 200 },
+      evmVersion: "cancun",
+    },
+  },
+  paths: {
+    root: "..",
+    sources: "contracts",
+    tests: "tests/contracts",
+    cache: "deploy/cache",
+    artifacts: "deploy/artifacts",
   },
   networks: {
     hardhat: {},

deploy/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "@kcolbchain/meridian-contracts",
+  "version": "0.1.0",
+  "scripts": {
+    "compile": "hardhat --config deploy/hardhat.config.js compile",
+    "test": "hardhat --config deploy/hardhat.config.js test",
+    "deploy:local": "hardhat --config deploy/hardhat.config.js run deploy/deploy.js --network localhost",
+    "deploy:base-sepolia": "hardhat --config deploy/hardhat.config.js run deploy/deploy.js --network base-sepolia",
+    "deploy:op-sepolia": "hardhat --config deploy/hardhat.config.js run deploy/deploy.js --network op-sepolia",
+    "deploy:fuji": "hardhat --config deploy/hardhat.config.js run deploy/deploy.js --network fuji"
+  },
+  "dependencies": {
+    "@openzeppelin/contracts": "^5.0.0"
+  },
+  "devDependencies": {
+    "@nomicfoundation/hardhat-toolbox": "^4.0.0",
+    "hardhat": "^2.19.0"
+  }
+}