Clean up docs and finish mobile QA

## Problem
The README now documents current status, but lower sections still contain older Arlington/demo wording and the native mobile workflow needs final post-publish validation.

## Goal
Clean up docs and finish mobile QA once the production data pipeline is complete.

## Acceptance Criteria
- README consistently refers to Travis County production data except where explicitly describing fallback fixtures.
- APK testing instructions include exact build/install/run steps and expected realtime behavior.
- Android debug APK is rebuilt after the final web bundle.
- iOS instructions are checked for Xcode availability and expected simulator/device path.
- Known limitations and remaining operational steps are documented clearly.

Start with the README and the existing APK build/install/run instructions, then review the iOS instructions for the Xcode and simulator/device path. After the production data pipeline and final web bundle are complete, rebuild the Android debug APK, validate realtime behavior, and document limitations and remaining operational steps.

Written by the indexing model from the issue text.