fix(FN-2539): preserve dashboard API compatibility and harden proxy wildcard routing

- Replace app/api.ts with a compatibility barrel that re-exports the legacy client API surface from app/api/legacy.ts
- Move the existing dashboard API implementation into app/api/legacy.ts and update static-analysis tests to include the new module path
- Update proxy wildcard routing to use /proxy/:nodeId/{*splat}, keeping explicit proxy handlers ahead of the fallback route
- Reject proxying to local nodes with a consistent 400 response and expand proxy route tests plus route-ordering compatibility notes

packages/dashboard/app/__tests__/agent-runs-ui.test.ts

@@ -10,11 +10,12 @@ const agentsViewPath = path.join(__dirname, "../components/AgentsView.tsx");
 const agentDetailViewPath = path.join(__dirname, "../components/AgentDetailView.tsx");
 const agentRunHistoryPath = path.join(__dirname, "../components/AgentRunHistory.tsx");
 const apiPath = path.join(__dirname, "../api.ts");
+const apiLegacyPath = path.join(__dirname, "../api/legacy.ts");
 
 const agentsViewContent = fs.readFileSync(agentsViewPath, "utf-8");
 const agentDetailViewContent = fs.readFileSync(agentDetailViewPath, "utf-8");
 const agentRunHistoryContent = fs.readFileSync(agentRunHistoryPath, "utf-8");
-const apiContent = fs.readFileSync(apiPath, "utf-8");
+const apiContent = `${fs.readFileSync(apiPath, "utf-8")}\n${fs.existsSync(apiLegacyPath) ? fs.readFileSync(apiLegacyPath, "utf-8") : ""}`;
 
 describe("Agent runs UI — static analysis", () => {
   describe("startAgentRun API function", () => {