#23753: docs: fix grammar "a OpenClaw" → "an OpenClaw" across 8 files

## Summary - Fixed 10 instances of incorrect article "a OpenClaw" → "an OpenClaw" across 8 documentation files - "OpenClaw" starts with a vowel sound, so the correct indefinite article is "an" ### Files changed: - `docs/start/showcase.md` - `docs/install/migrating.md` (2 instances) - `docs/cli/acp.md` (2 instances) - `docs/tools/browser.md` - `docs/tools/clawhub.md` - `docs/plugins/manifest.md` - `docs/platforms/mac/remote.md` - `docs/platforms/mac/release.md` ## Test plan - [x] Verified each change is a simple article correction - [x] No logic or behavior changes <!-- greptile_comment --> <h3>Greptile Summary</h3> Simple grammar correction changing "a OpenClaw" to "an OpenClaw" across 8 documentation files. Since "OpenClaw" starts with a vowel sound, the correct indefinite article is "an". All changes are purely cosmetic and improve the documentation's grammatical correctness without affecting any logic or behavior. <h3>Confidence Score: 5/5</h3> - This PR is completely safe to merge with no risk - Perfect score because this is a trivial documentation grammar fix with no code changes, no logic changes, and no impact on functionality. The changes are consistent, correct, and improve documentation quality. - No files require special attention _{Last reviewed commit: cd5024e} <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->