feat(a11y): WCAG 2.2 AA accessibility compliance (#209)

* feat(a11y): add i18n keys for ARIA labels and screen reader text

* fix(security): harden API against pentest findings

- Default TRUST_PROXY=false to prevent XFF rate limit bypass (PT-01)
- Return 400 instead of 500 on malformed JSON input (PT-03)
- Default MAX_PIPELINE_STEPS=20 to prevent DoS (PT-04)
- Validate clientJobId length (max 128) across all routes (PT-06)
- Add security headers to all reply.hijack() streaming responses (PT-07)
- Sanitize usernames in audit log to prevent stored XSS (PT-08)
- Block TRACE method with 405 response (PT-10)
- Add 429 RateLimited response to OpenAPI spec (PT-12)
- Default MAX_SVG_SIZE_MB=50 to limit SVGZ decompression (PT-13)
- Pin Dockerfile base images by digest
- Sanitize OIDC IdP error and sub claim in audit log
- Sync Docker compose/Dockerfile defaults with env.ts

* feat(a11y): convert all hardcoded aria-labels to i18n keys

Replace 49 hardcoded aria-label="..." strings across 25 files with
their corresponding t.a11y.* and t.common.* i18n references. Add
useTranslation import and hook call to 15 components that lacked it.
Zero hardcoded aria-labels remain in the codebase.

* feat(a11y): add aria-labels to icon-only buttons, aria-hidden on decorative icons, sr-only status text

* feat(a11y): add aria-live regions for processing status announcements

* feat(a11y): add skip-nav link, route announcer, main content landmark, and page h1 elements

* feat(a11y): add prefers-reduced-motion support, preserve functional spinners

* feat(a11y): add useFocusTrap hook for modal focus management

* feat(a11y): add focus trapping and dialog roles to all modals

* feat(a11y): add toggle switch roles, form labels, and error association

* fix(a11y): fix contrast failures, touch targets, and add nav landmark to sidebar

* fix(a11y): add role=switch to remaining toggle buttons found in verification sweep

apps/web/src/components/common/route-announcer.tsx

@@ -0,0 +1,48 @@
+import { useEffect, useRef } from "react";
+import { useLocation } from "react-router-dom";
+
+export function RouteAnnouncer() {
+  const location = useLocation();
+  const isFirstRender = useRef(true);
+  const announcerRef = useRef<HTMLDivElement>(null);
+
+  useEffect(() => {
+    if (isFirstRender.current) {
+      isFirstRender.current = false;
+      return;
+    }
+
+    const timer = setTimeout(() => {
+      const h1 = document.querySelector("h1");
+      if (h1) {
+        if (!h1.hasAttribute("tabindex")) {
+          h1.setAttribute("tabindex", "-1");
+        }
+        h1.focus({ preventScroll: true });
+        if (announcerRef.current) {
+          announcerRef.current.textContent = h1.textContent || "";
+        }
+      } else {
+        const main = document.getElementById("main-content");
+        if (main) {
+          if (!main.hasAttribute("tabindex")) {
+            main.setAttribute("tabindex", "-1");
+          }
+          main.focus({ preventScroll: true });
+        }
+      }
+    }, 300);
+
+    return () => clearTimeout(timer);
+  }, [location.pathname]);
+
+  return (
+    <div
+      ref={announcerRef}
+      className="sr-only"
+      aria-live="polite"
+      aria-atomic="true"
+      role="status"
+    />
+  );
+}