feat: add frontend features store and FEATURE_NOT_INSTALLED error handling

Add Zustand features store for tracking AI feature bundle state with
fetch, refresh, isToolInstalled, and getBundleForTool methods. Extend
parseApiError to return structured FeatureNotInstalledError objects
when the backend returns FEATURE_NOT_INSTALLED, and handle them in
both tool and pipeline processor hooks with user-friendly messages.

apps/web/src/stores/features-store.ts

@@ -0,0 +1,48 @@
+import type { FeatureBundleState } from "@ashim/shared";
+import { TOOL_BUNDLE_MAP } from "@ashim/shared";
+import { create } from "zustand";
+import { apiGet } from "@/lib/api";
+
+interface FeaturesState {
+  bundles: FeatureBundleState[];
+  loaded: boolean;
+  fetch: () => Promise<void>;
+  refresh: () => Promise<void>;
+  isToolInstalled: (toolId: string) => boolean;
+  getBundleForTool: (toolId: string) => FeatureBundleState | null;
+}
+
+export const useFeaturesStore = create<FeaturesState>((set, get) => ({
+  bundles: [],
+  loaded: false,
+
+  fetch: async () => {
+    if (get().loaded) return;
+    try {
+      const data = await apiGet<{ bundles: FeatureBundleState[] }>("/v1/features");
+      set({ bundles: data.bundles, loaded: true });
+    } catch {
+      set({ loaded: true });
+    }
+  },
+
+  refresh: async () => {
+    try {
+      const data = await apiGet<{ bundles: FeatureBundleState[] }>("/v1/features");
+      set({ bundles: data.bundles, loaded: true });
+    } catch {}
+  },
+
+  isToolInstalled: (toolId: string) => {
+    const bundleId = TOOL_BUNDLE_MAP[toolId];
+    if (!bundleId) return true;
+    const bundle = get().bundles.find((b) => b.id === bundleId);
+    return bundle?.status === "installed";
+  },
+
+  getBundleForTool: (toolId: string) => {
+    const bundleId = TOOL_BUNDLE_MAP[toolId];
+    if (!bundleId) return null;
+    return get().bundles.find((b) => b.id === bundleId) ?? null;
+  },
+}));