Detailed wiki content repair: Setup

Setup.md

@@ -0,0 +1,23 @@
+# Setup
+
+## Proven Setup Signals
+
+| Signal | Detail |
+|---|---|
+| platformio.ini | envs=seeed_xiao_esp32s3; boards=seeed_xiao_esp32s3; frameworks=arduino |
+| README files | README.md |
+
+## Setup Path
+
+- Use PlatformIO for firmware builds; confirm environment and board before flashing.
+
+## Environment Rules
+
+- Keep local secrets out of Git.
+- Put generated build output outside source control.
+- Prefer a clean checkout when validating setup instructions.
+- Record the exact command that works in the readiness issue before closing it.
+
+## Current Gaps
+
+- No setup gaps were inferred from inspected evidence.