chore(codegen): wire wagmi ABI codegen against smart-contracts submodule

- wagmi.config.ts: read ABIs from p2pix-smart-contracts/artifacts/contracts
  (P2Pix, Reputation, MockToken) and emit src/generated.ts with the
  @wagmi/cli actions plugin
- package.json: add scripts
  * contracts:compile — installs submodule deps + runs `hardhat compile`
  * wagmi:gen — runs @wagmi/cli to (re)generate src/generated.ts
  * prewagmi:gen — chains contracts:compile before wagmi:gen
  * prestart — runs wagmi:gen, so `bun start` always has fresh ABIs
- .gitignore: ignore src/generated.ts (regenerated on every prestart)

Note: GraphQL/subgraph codegen is intentionally out of scope here — it
will land in its own branch.

.gitignore

@@ -29,4 +29,7 @@ vendor/
 *.sw?
 .vercel
 
-.env
+.env
+
+# Codegen output (regenerated by `bun run wagmi:gen`, runs on prestart)
+src/generated.ts