chore(codegen): keep src/blockchain/abi.ts as wagmi output + infra polish

Path revert (reduces churn / preserves existing imports):
- wagmi.config.ts: out -> src/blockchain/abi.ts (was src/generated.ts)
- Restore the 4 import sites (sellerMethods, events, provider,
  BuyerSearchComponent) to import from './abi' / '@/blockchain/abi'
- .gitignore: ignore src/blockchain/abi.ts (was src/generated.ts)

The file keeps its original location and is no longer committed — it is
regenerated from the smart-contracts submodule artifacts on every
prestart via `bun run wagmi:gen`.

Infra polish:
- package.json: contracts:compile uses pushd/popd (instead of cd) so the
  shell returns to the project root after the submodule build, even when
  the script is the leaf of a longer chain
- .gitmodules: zkPix submodule pinned to `dev`

wagmi.config.ts

@@ -16,7 +16,7 @@ const loadAbi = (relPath: string) => {
 };
 
 export default defineConfig({
-  out: 'src/generated.ts',
+  out: 'src/blockchain/abi.ts',
   contracts: [
     { name: 'P2Pix', abi: loadAbi('p2pix.sol/P2PIX.json') as never },
     {