[nexus] feat(19-02): adapter-aware route handlers with agentId resolution

- Add resolveSkillsDirForAgent helper to skill-registry.ts and skill-registry-groups.ts
- Install route accepts agentId in body (not agentSkillsDir)
- Uninstall route accepts agentId as query param; returns 403 for native skills
- Rollback route accepts agentId in body (not agentSkillsDir)
- Group assign/remove routes resolve dir from URL agentId param
- List agent skills route calls syncHermesNativeSkills for hermes_local agents
- skillRegistryRoutes(db) and skillGroupRoutes(db) factory signatures updated
- app.ts passes db to both route factories

server/src/routes/skill-registry-groups.ts

@@ -7,9 +7,22 @@ import { skillGroupService } from "../services/skill-registry-groups.js";
 import { skillRegistryService } from "../services/skill-registry.js";
 import { assertBoard } from "./authz.js";
 
-/** Default skills directory when client doesn't provide one */
-function defaultSkillsDir(): string {
-  return path.join(os.homedir(), ".claude", "skills");
+/**
+ * Resolves the agentSkillsDir for a given agentId by looking up the agent's
+ * adapter type and calling resolveAdapterSkillConfig. Throws with a status
+ * property so route handlers can forward the correct HTTP status code.
+ */
+async function resolveSkillsDirForAgent(db: Db, agentId: string): Promise<string> {
+  const agent = await agentService(db).getById(agentId);
+  if (!agent) throw Object.assign(new Error("Agent not found"), { status: 404 });
+  const config = resolveAdapterSkillConfig(agent.adapterType);
+  if (!config.supportsInstall || !config.skillDir) {
+    throw Object.assign(
+      new Error(config.unsupportedReason ?? "Adapter does not support skill install"),
+      { status: 422 },
+    );
+  }
+  return config.skillDir.replace(/^~/, os.homedir());
 }
 
 /**