refactor: migrate kraiken-lib to explicit subpath imports (BREAKING CHANGE) (#89)

Removes the barrel export pattern in favor of explicit subpath imports
for better tree-shaking and clearer dependencies.

## Breaking Changes
- Removed `src/helpers.ts` barrel export
- Removed `./helpers` from package.json exports
- Root `kraiken-lib` import now raises build errors
- Consumers MUST use explicit subpaths:
  - `kraiken-lib/abis` - Contract ABIs
  - `kraiken-lib/staking` - Staking helpers
  - `kraiken-lib/snatch` - Snatch selection
  - `kraiken-lib/ids` - Position ID utilities
  - `kraiken-lib/subgraph` - Byte conversion utilities
  - `kraiken-lib/taxRates` - Tax rate constants
  - `kraiken-lib/version` - Version validation

## Changes
- kraiken-lib:
  - Bumped version to 1.0.0 (breaking change)
  - Updated src/index.ts to raise build errors
  - Added backward-compatible ABI aliases (KraikenAbi, StakeAbi)
  - Updated all test files to use .js extensions and new imports
  - Updated documentation (README, AGENTS.md)

- Consumer updates:
  - services/ponder: Updated ponder.config.ts to use kraiken-lib/abis
  - web-app: Updated all imports to use subpaths
    - composables/usePositions.ts: kraiken-lib/subgraph
    - contracts/harb.ts: kraiken-lib/abis
    - contracts/stake.ts: kraiken-lib/abis

## Migration Guide
```typescript
// OLD
import { getSnatchList } from 'kraiken-lib/helpers';
import { KraikenAbi } from 'kraiken-lib';

// NEW
import { getSnatchList } from 'kraiken-lib/snatch';
import { KraikenAbi } from 'kraiken-lib/abis';
```

Fixes #86

Co-authored-by: openhands <openhands@all-hands.dev>
Reviewed-on: https://codeberg.org/johba/harb/pulls/89

tests/e2e/02-max-stake-all-tax-rates.spec.ts

@@ -138,14 +138,14 @@ test.describe('Max Stake All Tax Rates', () => {
           id: 1,
           method: 'eth_call',
           params: [{
-            to: '0xe527ddac2592faa45884a0b78e4d377a5d3df8cc', // KRK token
+            to: STACK_CONFIG.contracts.Kraiken, // KRK token from deployments
             data: `0x70a08231000000000000000000000000${ACCOUNT_ADDRESS.slice(2)}` // balanceOf(address)
           }, 'latest']
         })
       });
 
       const balanceData = await balanceResponse.json();
-      const balance = BigInt(balanceData.result || '0');
+      const balance = BigInt(balanceData.result || '0x0');
       console.log(`[TEST] KRK balance: ${balance.toString()} wei`);
       expect(balance).toBeGreaterThan(0n);