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/WhaleOptimizer.sol

@@ -1,8 +1,8 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 pragma solidity ^0.8.19;
 
-import {Kraiken} from "../../src/Kraiken.sol";
-import {Stake} from "../../src/Stake.sol";
+import { Kraiken } from "../../src/Kraiken.sol";
+import { Stake } from "../../src/Stake.sol";
 
 /**
  * @title WhaleOptimizer
@@ -20,14 +20,14 @@ contract WhaleOptimizer {
 
     function getLiquidityParams() external pure returns (uint256, uint256, uint24, uint256) {
         return (
-            1e17,  // capitalInefficiency: 10% (very aggressive)
+            1e17, // capitalInefficiency: 10% (very aggressive)
             95e16, // anchorShare: 95% (massive anchor position)
-            10,    // anchorWidth: 10 (extremely narrow)
-            5e16   // discoveryDepth: 5% (minimal discovery)
+            10, // anchorWidth: 10 (extremely narrow)
+            5e16 // discoveryDepth: 5% (minimal discovery)
         );
     }
 
     function getDescription() external pure returns (string memory) {
         return "Whale Market - Massive concentrated liquidity";
     }
-}
+}