analytics: Update labels for mobile apps for Flutter launch.

[laurynmm]

Updates the labels in the messages by client chart so that the Flutter app is no longer labeled as beta and the React Native app is now labeled as old. The older Android and iOS apps are now labeled as ancient.

Part of: zulip/zulip-flutter#715.
Relevant CZO discussion: #api design > zulip-flutter in analytics client chart @ 💬

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Screenshots and screen captures:

from Analytics realm in dev environment

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Self-review checklist

• Self-reviewed the changes for clarity and maintainability
  (variable names, code reuse, readability, etc.).

Communicate decisions, questions, and potential concerns.

• Explains differences from previous plans (e.g., issue description).
• Highlights technical choices and bugs encountered.
• Calls out remaining decisions and concerns.
• Automated tests verify logic where appropriate.

Individual commits are ready for review (see commit discipline).

• Each commit is a coherent idea.
• Commit message(s) explain reasoning and motivation for changes.

Completed manual review and testing of the following:

• Visual appearance of the changes.
• Responsiveness and internationalization.
• Strings and tooltips.
• End-to-end functionality of buttons, interactions and flows.
• Corner cases, error conditions, and easily imagined bugs.

[zulipbot]

Hello @zulip/server-analytics members, this pull request was labeled with the "area: analytics" label, so you may want to check it out!

[laurynmm]

CI failure installing dependencies is not related to changes in this PR.

[laurynmm]

Updates:

• The new label for the React Native app is "Old mobile app (React Native)"
• The new label for the older mobile apps are "Ancient Android app" and "Ancient iOS app"

Screenshot has been updated in main PR comment for these updates.

[timabbott]

Meged, thanks @laurynmm!