feat(FN-2166): persist dev server script configuration across sessions

- Extend dev server store with config defaults, normalization, and JSON persistence alongside runtime state.
- Add GET/PUT /api/dev-server/config endpoints with strict request validation for nullable fields and preview URLs.
- Add dashboard API helpers plus a useDevServerConfig hook to load and update selected script, source, command, and preview override.
- Update DevServerView and styles to support saved script selection, change/clear actions, and synchronized command/preview inputs.
- Expand dev server store/routes/component tests and document the config endpoint in architecture docs.

packages/dashboard/app/hooks/useDevServerConfig.ts

@@ -0,0 +1,125 @@
+import { useCallback, useEffect, useRef, useState } from "react";
+import {
+  fetchDevServerConfig,
+  saveDevServerConfig,
+  type DevServerConfig,
+} from "../api";
+
+interface SelectableDevServerScript {
+  name: string;
+  command: string;
+  source: string;
+}
+
+export interface UseDevServerConfigResult {
+  config: DevServerConfig | null;
+  loading: boolean;
+  error: string | null;
+  selectScript: (script: SelectableDevServerScript) => Promise<void>;
+  clearSelection: () => Promise<void>;
+  setPreviewUrlOverride: (url: string | null) => Promise<void>;
+  refresh: () => Promise<void>;
+}
+
+function normalizeError(error: unknown): string {
+  return error instanceof Error ? error.message : String(error);
+}
+
+export function useDevServerConfig(projectId?: string): UseDevServerConfigResult {
+  const [config, setConfig] = useState<DevServerConfig | null>(null);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const versionRef = useRef(0);
+
+  const refresh = useCallback(async () => {
+    const version = versionRef.current + 1;
+    versionRef.current = version;
+    setLoading(true);
+
+    try {
+      const nextConfig = await fetchDevServerConfig(projectId);
+      if (versionRef.current !== version) {
+        return;
+      }
+
+      setConfig(nextConfig);
+      setError(null);
+    } catch (refreshError) {
+      if (versionRef.current !== version) {
+        return;
+      }
+
+      setError(normalizeError(refreshError));
+    } finally {
+      if (versionRef.current === version) {
+        setLoading(false);
+      }
+    }
+  }, [projectId]);
+
+  const savePartial = useCallback(async (partial: Partial<DevServerConfig>) => {
+    const version = versionRef.current + 1;
+    versionRef.current = version;
+    setLoading(true);
+    setError(null);
+
+    try {
+      const updated = await saveDevServerConfig(partial, projectId);
+      if (versionRef.current !== version) {
+        return;
+      }
+
+      setConfig(updated);
+    } catch (saveError) {
+      if (versionRef.current !== version) {
+        return;
+      }
+
+      const message = normalizeError(saveError);
+      setError(message);
+      throw saveError;
+    } finally {
+      if (versionRef.current === version) {
+        setLoading(false);
+      }
+    }
+  }, [projectId]);
+
+  const selectScript = useCallback(async (script: SelectableDevServerScript) => {
+    await savePartial({
+      selectedScript: script.name,
+      selectedSource: script.source,
+      selectedCommand: script.command,
+      selectedAt: new Date().toISOString(),
+    });
+  }, [savePartial]);
+
+  const clearSelection = useCallback(async () => {
+    await savePartial({
+      selectedScript: null,
+      selectedSource: null,
+      selectedCommand: null,
+      selectedAt: null,
+    });
+  }, [savePartial]);
+
+  const setPreviewUrlOverride = useCallback(async (url: string | null) => {
+    await savePartial({
+      previewUrlOverride: url,
+    });
+  }, [savePartial]);
+
+  useEffect(() => {
+    void refresh();
+  }, [refresh]);
+
+  return {
+    config,
+    loading,
+    error,
+    selectScript,
+    clearSelection,
+    setPreviewUrlOverride,
+    refresh,
+  };
+}