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/IconBadge.tsx

@@ -0,0 +1,40 @@
+import type { ReactNode } from "react";
+import "@shared/components/IconBadge.css";
+
+export type IconBadgeAccent = "blue" | "purple" | "green" | "amber" | "red";
+
+export interface IconBadgeProps {
+  children: ReactNode;
+  /** Tone tint. Defaults to blue. */
+  accent?: IconBadgeAccent;
+  size?: "sm" | "md";
+  className?: string;
+}
+
+/**
+ * A glyph in a rounded, tone-tinted square — the recurring "category icon box"
+ * motif used by panel headers, summaries and list leads. Centralises the tint
+ * so every consumer shares one treatment.
+ */
+export function IconBadge({
+  children,
+  accent = "blue",
+  size = "md",
+  className,
+}: IconBadgeProps) {
+  return (
+    <span
+      className={[
+        "sui-iconbadge",
+        `sui-iconbadge--${accent}`,
+        `sui-iconbadge--${size}`,
+        className ?? "",
+      ]
+        .filter(Boolean)
+        .join(" ")}
+      aria-hidden
+    >
+      {children}
+    </span>
+  );
+}