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/VWAPTracker.sol

@@ -7,7 +7,7 @@ import "@openzeppelin/utils/math/Math.sol";
  * @title VWAPTracker
  * @notice Abstract contract for tracking Volume Weighted Average Price (VWAP) data
  * @dev Provides VWAP calculation and storage functionality that can be inherited by other contracts
- * 
+ *
  * Key features:
  * - Volume-weighted average with data compression (max 1000x compression)
  * - Prevents dormant whale manipulation through historical price memory
@@ -31,7 +31,7 @@ abstract contract VWAPTracker {
         // assuming FEE is 1%
         uint256 volume = fee * 100;
         uint256 volumeWeightedPriceX96 = currentPriceX96 * volume;
-        
+
         // ULTRA-RARE EDGE CASE: Check if the new data itself would overflow even before adding
         // This can only happen with impossibly large transactions (>10,000 ETH + $billion token prices)
         if (volumeWeightedPriceX96 > type(uint256).max / 2) {
@@ -46,18 +46,18 @@ abstract contract VWAPTracker {
             // Find the MINIMUM compression factor needed to prevent overflow
             uint256 maxSafeValue = type(uint256).max / 10 ** 6; // Leave substantial room for future data
             uint256 compressionFactor = (cumulativeVolumeWeightedPriceX96 / maxSafeValue) + 1;
-            
+
             // Cap maximum compression to preserve historical "eternal memory"
             // Even in extreme cases, historical data should retain significant weight
             if (compressionFactor > 1000) {
                 compressionFactor = 1000; // Maximum 1000x compression to preserve history
             }
-            
+
             // Ensure minimum compression effectiveness
             if (compressionFactor < 2) {
                 compressionFactor = 2; // At least 2x compression when triggered
             }
-            
+
             // Compress both values by the same minimal factor
             cumulativeVolumeWeightedPriceX96 = cumulativeVolumeWeightedPriceX96 / compressionFactor;
             cumulativeVolume = cumulativeVolume / compressionFactor;