fix: reliable, self-healing AI feature-bundle installs (#472)

Make on-demand AI feature-bundle installs reliable and self-healing, closing
the failure modes behind most "some tool doesn't work" reports.

Multi-bundle installs: tools needing more than one bundle (Passport Photo,
Enhance Faces) install every required bundle from one action and stay
not-installed until all are present. Verified across all 19 AI tools.

Downloads: self-heal the accelerated Hugging Face (Xet) client so an upgraded
venv no longer silently falls back to slow urllib; restart instead of
corrupting a resumed partial when a proxy ignores Range and returns 200;
verify the completed size; fail fast on disk-full and HTTP 4xx; retry
transient errors five times; add hf_transfer fallback and document Xet egress.

Install integrity: crash-atomic venv writes so a killed or out-of-space
install can no longer tear the shared venv and break other tools; a boot
breadcrumb reseeds a torn venv to a clean state automatically; a post-install
smoke import test refuses to record a bundle whose libraries cannot load; an
install watchdog stops a wedged installer that would otherwise hold the venv
writer lock forever.

Adds unit and end-to-end tests for every failure mode above.

tests/unit/web/tool-card-pin.test.tsx

@@ -1,9 +1,11 @@
 // @vitest-environment jsdom
+import type { FeatureBundleState } from "@snapotter/shared";
 import { TOOLS } from "@snapotter/shared";
 import { cleanup, fireEvent, render, screen } from "@testing-library/react";
 import { MemoryRouter } from "react-router-dom";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { ToolCard } from "@/components/common/tool-card";
+import { useFeaturesStore } from "@/stores/features-store";
 import { usePinnedToolsStore } from "@/stores/pinned-tools-store";
 
 // Make the store's optimistic persistence a no-op so the test stays server-free.
@@ -14,6 +16,23 @@ vi.mock("@/lib/api", () => ({
 
 const resize = TOOLS.find((tool) => tool.id === "resize");
 if (!resize) throw new Error("resize tool missing from TOOLS");
+const passportPhoto = TOOLS.find((tool) => tool.id === "passport-photo");
+if (!passportPhoto) throw new Error("passport-photo tool missing from TOOLS");
+
+function makeBundleState(overrides: Partial<FeatureBundleState> = {}): FeatureBundleState {
+  return {
+    id: "background-removal",
+    name: "Background Removal",
+    description: "Remove backgrounds",
+    status: "not_installed",
+    installedVersion: null,
+    estimatedSize: "4-5 GB",
+    enablesTools: ["remove-background", "passport-photo"],
+    progress: null,
+    error: null,
+    ...overrides,
+  };
+}
 
 afterEach(cleanup);
 
@@ -24,6 +43,16 @@ beforeEach(() => {
     loaded: true,
     loadError: false,
   });
+  useFeaturesStore.setState({
+    bundles: [],
+    loaded: true,
+    loadError: false,
+    installing: {},
+    errors: {},
+    queued: [],
+    installAllActive: false,
+    startTimes: {},
+  });
 });
 
 function renderCard(showPin: boolean) {
@@ -56,3 +85,28 @@ describe("ToolCard pin button", () => {
     expect(usePinnedToolsStore.getState().pinnedTools).toEqual([]);
   });
 });
+
+describe("ToolCard AI bundle status", () => {
+  it("treats multi-bundle tools as not installed when an extra bundle is missing", () => {
+    useFeaturesStore.setState({
+      bundles: [
+        makeBundleState({ id: "background-removal", status: "installed" }),
+        makeBundleState({
+          id: "face-detection",
+          name: "Face Detection",
+          status: "not_installed",
+          enablesTools: ["blur-faces", "red-eye-removal", "smart-crop"],
+        }),
+      ],
+    });
+
+    const { container } = render(
+      <MemoryRouter>
+        <ToolCard tool={passportPhoto} variant="descriptive" />
+      </MemoryRouter>,
+    );
+
+    // One SVG is the tool icon, the second is the missing-AI-bundle indicator.
+    expect(container.querySelectorAll("svg")).toHaveLength(2);
+  });
+});