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.tsx

@@ -0,0 +1,43 @@
+import "@shared/components/StepIndicator.css";
+
+export interface StepIndicatorProps {
+  /** Total number of steps. */
+  total: number;
+  /** Current step, 1-based. */
+  current: number;
+  size?: "sm" | "md";
+  className?: string;
+}
+
+/**
+ * A segmented step/progress rail for multi-step flows (wizards, onboarding).
+ * Segments before `current` read as completed, the `current` segment is
+ * emphasised, and the rest are upcoming.
+ */
+export function StepIndicator({
+  total,
+  current,
+  size = "md",
+  className,
+}: StepIndicatorProps) {
+  return (
+    <div
+      className={["sui-steps", `sui-steps--${size}`, className ?? ""]
+        .filter(Boolean)
+        .join(" ")}
+      role="progressbar"
+      aria-valuemin={1}
+      aria-valuemax={total}
+      aria-valuenow={current}
+    >
+      {Array.from({ length: total }, (_, i) => {
+        const step = i + 1;
+        const state =
+          step < current ? "done" : step === current ? "current" : "upcoming";
+        return (
+          <span key={step} className="sui-steps__bar" data-state={state} />
+        );
+      })}
+    </div>
+  );
+}