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/ChipFlow.tsx

@@ -0,0 +1,47 @@
+import { Fragment } from "react";
+import type { ReactNode } from "react";
+import { Chip } from "@shared/components/Chip";
+import type { ChipTone, ChipSize } from "@shared/components/Chip";
+import "@shared/components/ChipFlow.css";
+
+export interface ChipFlowProps {
+  /** Items rendered as chips, in order. */
+  items: ReactNode[];
+  /** `arrow` joins chips with a → connector (pipeline look); `none` just wraps. */
+  separator?: "arrow" | "none";
+  tone?: ChipTone;
+  size?: ChipSize;
+  className?: string;
+}
+
+/**
+ * A sequence of {@link Chip}s, optionally joined by arrows to read as a
+ * pipeline (A → B → C). Use `separator="arrow"` for flows, `none` for a plain
+ * wrapped chip list.
+ */
+export function ChipFlow({
+  items,
+  separator = "none",
+  tone = "neutral",
+  size = "sm",
+  className,
+}: ChipFlowProps) {
+  return (
+    <div
+      className={["sui-chipflow", className ?? ""].filter(Boolean).join(" ")}
+    >
+      {items.map((item, i) => (
+        <Fragment key={i}>
+          {i > 0 && separator === "arrow" && (
+            <span className="sui-chipflow__sep" aria-hidden>
+              →
+            </span>
+          )}
+          <Chip tone={tone} size={size}>
+            {item}
+          </Chip>
+        </Fragment>
+      ))}
+    </div>
+  );
+}