feat(policies): backend-driven policy enforcement (frontend) (#6598)

## Summary
Adds the **Policies** feature (proprietary, behind the
`POLICIES_ENABLED` flag): backend-driven enforcement that runs a fixed
tool pipeline on documents, docked in the right tool sidebar alongside
Tools.

## Highlights
- **Policy catalog** — 5 categories; **Security** is wired (redact PII +
sanitize), the others are marked "Coming soon".
- **Backend as source of truth** — policies persist via the Policies
engine (`/api/v1/policies`), one policy per category, with a local cache
+ offline fallback.
- **Auto-run** — enabled policies run on every uploaded file: dispatch →
poll → import outputs into the workspace.
- **Security redact config** — PII preset dropdown + custom word/regex
entry + advanced options; tool params map to the backend endpoint
fields.
- **Activity feed** with retry on failures; **file badges** showing
which policies ran on a file (sidebar + files page), tinted to the
policy colour.
- Reuses the **Watched Folders** engine for each policy's backing
folder; policy-owned folders are filtered out of the Watched Folders UI.

## Notes
- Gated by `POLICIES_ENABLED` (true in proprietary, false in core) —
unreachable in the open-source build.
- Frontend-only diff; depends on the backend Policies engine and the
merged Watched Folders feature.

frontend/shared/components/StepIndicator.stories.tsx

@@ -0,0 +1,29 @@
+import type { Meta, StoryObj } from "@storybook/react-vite";
+import { StepIndicator } from "@shared/components/StepIndicator";
+
+const meta: Meta<typeof StepIndicator> = {
+  title: "Primitives/StepIndicator",
+  component: StepIndicator,
+  tags: ["autodocs"],
+  parameters: { layout: "padded" },
+  args: { total: 3, current: 2, size: "md" },
+  argTypes: {
+    current: { control: { type: "number", min: 1, max: 5 } },
+    total: { control: { type: "number", min: 1, max: 5 } },
+    size: { control: "inline-radio", options: ["sm", "md"] },
+  },
+  decorators: [
+    (S) => (
+      <div style={{ maxWidth: "20rem" }}>
+        <S />
+      </div>
+    ),
+  ],
+};
+export default meta;
+type Story = StoryObj<typeof StepIndicator>;
+
+export const Step1: Story = { args: { total: 3, current: 1 } };
+export const Step2: Story = { args: { total: 3, current: 2 } };
+export const Step3: Story = { args: { total: 3, current: 3 } };
+export const Small: Story = { args: { total: 4, current: 2, size: "sm" } };