Mirror: Spelling and phrasing mistakes in skills markdown

This mirrors Issue Tracker bug https://issuetracker.google.com/issues/515090590.

The original report flags spelling, capitalization, spacing, phrasing, heading, numbering, and JSON example issues across several Android skill Markdown files.

A proposed fix is available as a pull request against my fork because pull requests are currently restricted on this repository:

https://github.com/hamen/skills-1/pull/1

The fork PR fixes:
- Trade-offs wording in the Compose styles skill.
- JaCoCo capitalization and heading levels in the testing setup skill.
- Missing sentence spacing in the Perfetto SQL skill.
- R8 build-time performance phrasing.
- Stale Antigravity-specific wording in the Android CLI skill.
- Duplicate numbering in the Android interaction rules.
- Malformed JSON keys and missing quote in the journeys example.

Validation included in the branch:
- bash scripts/check_issue_515090590.sh
- git diff --check

cc @JoseAlcerreca

Review the Compose styles, testing setup, Perfetto SQL, Android CLI, Android interaction rules, and journeys Markdown changes described in the issue. Start by examining the proposed fork pull request and run bash scripts/check_issue_515090590.sh plus git diff --check; done means the listed spelling, phrasing, heading, numbering, and JSON issues are corrected and validation passes.

Written by the indexing model from the issue text.