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/App.tsx

@@ -4,6 +4,7 @@ import { BrowserRouter, Navigate, Route, Routes, useLocation } from "react-route
 import { Toaster, toast } from "sonner";
 import { ConnectionMonitor } from "./components/common/connection-monitor";
 import { KeyboardShortcutProvider } from "./components/common/keyboard-shortcut-provider";
+import { RouteAnnouncer } from "./components/common/route-announcer";
 import { I18nProvider } from "./contexts/i18n-context";
 import { useAuth } from "./hooks/use-auth";
 import { useMobile } from "./hooks/use-mobile";
@@ -221,6 +222,13 @@ export function App() {
         <ConnectionMonitor />
         <Toaster position={isMobile ? "top-center" : "bottom-right"} />
         <BrowserRouter>
+          <a
+            href="#main-content"
+            className="sr-only focus:not-sr-only focus:fixed focus:top-4 focus:left-4 focus:z-[100] focus:px-4 focus:py-2 focus:bg-primary focus:text-primary-foreground focus:rounded-lg focus:text-sm focus:font-medium focus:shadow-lg"
+          >
+            {en.a11y.skipToContent}
+          </a>
+          <RouteAnnouncer />
           <KeyboardShortcutProvider>
             <AuthGuard>
               <Suspense fallback={<PageLoader />}>