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/src/abstracts/PriceOracle.sol

@@ -1,8 +1,8 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 pragma solidity ^0.8.19;
 
-import "@uniswap-v3-core/interfaces/IUniswapV3Pool.sol";
 import "@openzeppelin/utils/math/SignedMath.sol";
+import "@uniswap-v3-core/interfaces/IUniswapV3Pool.sol";
 
 /**
  * @title PriceOracle
@@ -23,7 +23,7 @@ abstract contract PriceOracle {
     /// @return isStable True if price is within acceptable deviation from TWAP
     function _isPriceStable(int24 currentTick) internal view returns (bool isStable) {
         IUniswapV3Pool pool = _getPool();
-        
+
         uint32[] memory secondsAgo = new uint32[](2);
         secondsAgo[0] = PRICE_STABILITY_INTERVAL; // 5 minutes ago
         secondsAgo[1] = 0; // current block timestamp
@@ -51,15 +51,19 @@ abstract contract PriceOracle {
     /// @return isUp True if price moved up (relative to token ordering)
     /// @return isEnough True if movement amplitude is sufficient for recentering
     function _validatePriceMovement(
-        int24 currentTick, 
-        int24 centerTick, 
+        int24 currentTick,
+        int24 centerTick,
         int24 tickSpacing,
         bool token0isWeth
-    ) internal pure returns (bool isUp, bool isEnough) {
+    )
+        internal
+        pure
+        returns (bool isUp, bool isEnough)
+    {
         uint256 minAmplitude = uint24(tickSpacing) * 2;
 
         // Determine the correct comparison direction based on token0isWeth
         isUp = token0isWeth ? currentTick < centerTick : currentTick > centerTick;
         isEnough = SignedMath.abs(currentTick - centerTick) > minAmplitude;
     }
-}
+}