test(chat): add ContextUsageComponentsTest regression tests and clarify context tokens note

app/src/main/res/values/strings.xml

@@ -1435,7 +1435,7 @@
     <string name="context_completion_output">Completion (output)</string>
     <string name="context_compressed">compressed ×%1$s</string>
     <string name="context_prompt_input">Prompt (input)</string>
-    <string name="context_tokens_note">Prompt tokens reflect total context used by this session so far.</string>
+    <string name="context_tokens_note">Token counts below are cumulative session accounting and do not represent current context-window occupancy.</string>
     <string name="context_window">Context window</string>
     <string name="context_window_usage_unavailable">Context window usage unavailable</string>
     <string name="gif_play">Play GIF</string>