Add Solidity linting with solhint, Foundry formatter, and pre-commit hooks (#51)

## Changes

### Configuration
- Added .solhint.json with recommended rules + custom config
  - 160 char line length (warn)
  - Double quotes enforcement (error)
  - Explicit visibility required (error)
  - Console statements allowed (scripts/tests need them)
  - Gas optimization warnings enabled
  - Ignores test/helpers/, lib/, out/, cache/, broadcast/

- Added foundry.toml [fmt] section
  - 160 char line length
  - 4-space tabs
  - Double quotes
  - Thousands separators for numbers
  - Sort imports enabled

- Added .lintstagedrc.json for pre-commit auto-fix
  - Runs solhint --fix on .sol files
  - Runs forge fmt on .sol files

- Added husky pre-commit hook via lint-staged

### NPM Scripts
- lint:sol - run solhint
- lint:sol:fix - auto-fix solhint issues
- format:sol - format with forge fmt
- format:sol:check - check formatting
- lint / lint:fix - combined commands

### Code Changes
- Added explicit visibility modifiers (internal) to constants in scripts and tests
- Fixed quote style in DeployLocal.sol
- All Solidity files formatted with forge fmt

## Verification
- ✅ forge fmt --check passes
- ✅ No solhint errors (warnings only)
- ✅ forge build succeeds
- ✅ forge test passes (107/107)

resolves #44

Co-authored-by: johba <johba@harb.eth>
Reviewed-on: https://codeberg.org/johba/harb/pulls/51

onchain/test/mocks/RandomScenarioOptimizer.sol

@@ -5,28 +5,30 @@ import "./MockOptimizer.sol";
 
 contract RandomScenarioOptimizer is MockOptimizer {
     string private description;
-    
+
     function initialize(address _kraiken, address _stake) public override initializer {
         _changeAdmin(msg.sender);
         kraiken = Kraiken(_kraiken);
         stake = Stake(_stake);
     }
-    
+
     function setRandomParams(
         uint256 capitalInefficiency,
         uint256 anchorShare,
         uint24 anchorWidth,
         uint256 discoveryDepth,
         string memory scenarioDescription
-    ) external {
+    )
+        external
+    {
         _capitalInefficiency = capitalInefficiency;
         _anchorShare = anchorShare;
         _anchorWidth = anchorWidth;
         _discoveryDepth = discoveryDepth;
         description = scenarioDescription;
     }
-    
+
     function getDescription() external view returns (string memory) {
         return description;
     }
-}
+}