feat(ai): add a Reset AI Environment admin feature for the upgrade gap (#459)

Uninstalling a bundle only deletes its downloaded model weights, never the
shared venv's site-packages, so self-hosters who already hit an AI bundle
conflict (e.g. the scipy ABI strand) have no clean self-service path via
uninstall+reinstall: reinstalling just overlays corrected files on top of
stale ones. Adds POST /api/v1/admin/features/reset, which wipes
/data/ai/{venv,models,pip-cache}, resets installed.json, and reseeds a real
working venv from the image's baked /opt/venv (extracted docker/reseed-ai-venv.sh,
now shared with entrypoint.sh's existing base-venv-upgrade bootstrap instead
of duplicating that logic) -- leaving an empty venv directory here would
make the very next install fail with "spawn .../python3 ENOENT", caught by
testing this live rather than assuming it. Ships with a matching Settings UI
section (inline confirm, same pattern as per-bundle uninstall) and strings
across all 21 locales.

Verified against a real snapotter/snapotter:1.17.2 image migrated to 2.0.0,
with real multi-GB bundles installed (background-removal + OCR): confirmed
the migrated instance's inherited python3.11 venv (2.0.0 itself uses 3.12)
still imports the fixed scipy/numpy/paddleocr correctly, then reset + real
reinstall + actual tool execution (remove-background, verified output image)
all worked end-to-end.

tests/unit/web/features-store-expanded.test.ts

@@ -223,6 +223,49 @@ describe("useFeaturesStore (expanded)", () => {
     });
   });
 
+  describe("resetEnvironment", () => {
+    it("posts to the reset endpoint and refreshes bundles on success", async () => {
+      apiPostMock.mockResolvedValueOnce({});
+      apiGetMock.mockResolvedValueOnce({ bundles: [] });
+
+      await useFeaturesStore.getState().resetEnvironment();
+
+      expect(apiPostMock).toHaveBeenCalledWith("/v1/admin/features/reset", {});
+      expect(apiGetMock).toHaveBeenCalledWith("/v1/features");
+      expect(useFeaturesStore.getState().resetError).toBeNull();
+    });
+
+    it("clears stale installing/errors/queued state on success", async () => {
+      useFeaturesStore.setState({
+        installing: { ocr: { percent: 40, stage: "downloading" } },
+        errors: { ocr: "some old error" },
+        queued: ["ocr"],
+        startTimes: { ocr: Date.now() },
+      });
+      apiPostMock.mockResolvedValueOnce({});
+      apiGetMock.mockResolvedValueOnce({ bundles: [] });
+
+      await useFeaturesStore.getState().resetEnvironment();
+
+      const state = useFeaturesStore.getState();
+      expect(state.installing).toEqual({});
+      expect(state.errors).toEqual({});
+      expect(state.queued).toEqual([]);
+      expect(state.startTimes).toEqual({});
+    });
+
+    it("sets resetError on failure and does not refresh bundles", async () => {
+      apiPostMock.mockRejectedValueOnce(new Error("a bundle install is already in progress"));
+
+      await useFeaturesStore.getState().resetEnvironment();
+
+      expect(useFeaturesStore.getState().resetError).toBe(
+        "a bundle install is already in progress",
+      );
+      expect(apiGetMock).not.toHaveBeenCalled();
+    });
+  });
+
   describe("clearError", () => {
     it("does not affect other errors when clearing one", () => {
       useFeaturesStore.setState({