feat(tui): surface compression count in Ink status bar

Parity with the classic CLI status bar (PR #18579). The Python backend
already exposes 'compressions' on SessionUsageResponse; this wires it
through the Ink Usage type and renders 'cmp N' next to the duration
segment of StatusRule.

- types.ts Usage: add optional compressions field
- appChrome.tsx StatusRule: render 'cmp N' when > 0, color-tiered by
  pressure (muted <5, warn 5-9, error 10+)
- Plain text 'cmp' token (no emoji) matches PR #18579's original author
  rationale and avoids Ink layout drift from VS16 emoji width

ui-tui/src/components/appChrome.tsx

@@ -325,6 +325,14 @@ export function StatusRule({
               <SessionDuration startedAt={sessionStartedAt} />
             </Text>
           ) : null}
+          {typeof usage.compressions === 'number' && usage.compressions > 0 ? (
+            <Text color={t.color.muted}>
+              {' │ '}
+              <Text color={usage.compressions >= 10 ? t.color.error : usage.compressions >= 5 ? t.color.warn : t.color.muted}>
+                cmp {usage.compressions}
+              </Text>
+            </Text>
+          ) : null}
           <SpawnHud t={t} />
           {voiceLabel ? (
             <Text

ui-tui/src/types.ts

@@ -160,6 +160,7 @@ export interface SessionInfo {
 
 export interface Usage {
   calls: number
+  compressions?: number
   context_max?: number
   context_percent?: number
   context_used?: number