feat(terminal): add screen reader buffer and OS accessibility preferences

- Add debounced aria-live region that announces visible terminal text
  to screen readers (500ms throttle, non-empty trimmed rows only)
- Add role=application, aria-label, aria-roledescription to terminal
- Add prefers-reduced-motion listener: disables cursor blink animation
  and sets --terminal-reduce-motion CSS variable
- Add prefers-contrast: more media query with Canvas/CanvasText system
  color fallback
- Add visually hidden .terminal-screen-reader CSS utility
- Mark P7 complete in roadmap

style/tailwind.css

@@ -804,6 +804,20 @@
     background: rgb(125 211 252 / 14%);
   }
 
+
+  /* Screen-reader-only announcement region (visually hidden, accessible to AT). */
+  .terminal-screen-reader {
+    position: absolute;
+    width: 1px;
+    height: 1px;
+    margin: -1px;
+    padding: 0;
+    overflow: hidden;
+    clip: rect(0, 0, 0, 0);
+    white-space: nowrap;
+    border: 0;
+  }
+
   .terminal-measure {
     position: absolute;
     left: -9999px;
@@ -844,6 +858,36 @@
     color: var(--cowa-text-primary);
     line-height: 24px;
   }
+  /* Accessibility: respect OS-level motion preference. */
+  @media (prefers-reduced-motion: reduce) {
+    .terminal-cursor {
+      animation: none !important;
+    }
+    .terminal-screen,
+    .terminal-ime {
+      transition: none !important;
+    }
+  }
+
+  /* Accessibility: respect OS-level contrast preference. */
+  @media (prefers-contrast: more) {
+    .terminal-screen {
+      background: Canvas !important;
+      color: CanvasText !important;
+      border-color: CanvasText !important;
+    }
+    .terminal-text {
+      color: CanvasText !important;
+    }
+    .terminal-segment {
+      color: CanvasText !important;
+    }
+    .terminal-badge {
+      border: 1px solid CanvasText;
+    }
+  }
+
+
 
   .cowa-page-heading p {
     @apply m-0 pt-1 text-sm;