fix(modules): validate group module create per kind (Phase 4b review)

Adversarial-review finding: `create_group_script` validated every source
with `validate()` regardless of kind, so an imperatively-created group
module (`pic scripts deploy --group g --name kv --kind module`) skipped the
two gates every other module-write path enforces (app create/update in
api.rs, declarative apply in apply_service): the stricter `validate_module`
shape check and the `RESERVED_MODULE_NAMES` guard. A malformed-shape group
module was accepted at create (only failing later at import-resolve time)
and a reserved name (`kv`, `log`, …) slipped through.

Branch on kind to mirror the app path. Adds a journey asserting a reserved
group-module name is rejected.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/manager-core/src/group_scripts_api.rs

@@ -97,10 +97,25 @@ async fn create_group_script(
     )
     .await?;
 
-    // Phase 4b: group modules + imports are allowed. Imports resolve
-    // lexically from this group's chain at runtime (§5.5); the recorded
-    // edges feed the declarative dangling-import plan check.
-    let validated = s.validator.validate(&input.source)?;
+    // Phase 4b: group modules + imports are allowed. Validate per kind,
+    // mirroring the app-script create path (`api.rs`): a module gets the
+    // stricter shape check + the reserved-name guard; an endpoint the
+    // parse-only path. Without the kind branch a malformed-shape group
+    // module would be accepted here and only fail later at import time,
+    // and a reserved name (`kv`, `log`, …) would slip through. Imports
+    // resolve lexically from this group's chain at runtime (§5.5); the
+    // recorded edges feed the declarative dangling-import plan check.
+    let validated = if input.kind == ScriptKind::Module {
+        if crate::api::RESERVED_MODULE_NAMES.contains(&input.name.as_str()) {
+            return Err(GroupScriptsApiError::Invalid(format!(
+                "{:?} is a reserved module name (shadows a built-in SDK namespace)",
+                input.name
+            )));
+        }
+        s.validator.validate_module(&input.source)?
+    } else {
+        s.validator.validate(&input.source)?
+    };
     s.sandbox_ceiling
         .check(&input.sandbox)
         .map_err(|e| GroupScriptsApiError::Invalid(e.to_string()))?;