gnd: Create networks.json in init --from-contract

Previously, `gnd init --from-contract` would not create a networks.json
file, unlike `gnd init --from-example`. This meant users had to manually
create the networks.json configuration or experience errors when trying
to deploy to different networks.

Now, when scaffolding from a contract address, gnd creates a networks.json
file with the contract name, address, and start block configuration for
the specified network.

Issue: I5 from PR 6282 review feedback

Author: lutter

gnd/src/commands/init.rs

@@ -17,6 +17,7 @@ use anyhow::{anyhow, Context, Result};
 use clap::{Parser, ValueEnum};
 use graphql_parser::schema as gql;
 
+use crate::config::networks::update_networks_file;
 use crate::output::{step, with_spinner, Step};
 use crate::prompt::{
     get_subgraph_basename, prompt_directory_with_confirm, prompt_subgraph_slug_with_confirm,
@@ -362,6 +363,16 @@ async fn init_from_contract(opt: &InitOpt) -> Result<()> {
 
     generate_scaffold(&directory, &scaffold_options)?;
 
+    // Create networks.json with the contract configuration
+    let networks_path = directory.join("networks.json");
+    update_networks_file(
+        &networks_path,
+        network,
+        &contract_name,
+        address,
+        start_block,
+    )?;
+
     // Initialize git unless skipped
     if !opt.skip_git {
         let _ = init_git(&directory);

gnd/tests/cli_commands.rs

@@ -282,6 +282,20 @@ fn test_init_from_contract_with_abi() {
         manifest.contains("SimpleContract"),
         "Manifest should contain contract name"
     );
+
+    // Verify networks.json was created with contract config
+    let networks_path = subgraph_dir.join("networks.json");
+    assert!(networks_path.exists(), "networks.json should exist");
+
+    let networks: serde_json::Value =
+        serde_json::from_str(&fs::read_to_string(&networks_path).unwrap()).unwrap();
+    assert!(
+        networks["mainnet"]["SimpleContract"]["address"]
+            .as_str()
+            .unwrap()
+            .contains("0x5fbdb2315678afecb367f032d93f642f64180aa3"),
+        "networks.json should contain contract address"
+    );
 }
 
 #[test]