[ai] add Claude config

Author: pq

CLAUDE.md

@@ -0,0 +1,12 @@
+# Flutter IntelliJ Plugin — Claude Code Guide
+
+@.gemini/styleguide.md
+
+## Additional Rules
+
+- No I/O or heavy computation on the EDT (IntelliJ Threading Model).
+- All `AnAction` subclasses must be stateless (no mutable instance fields).
+- Use `io.flutter.logging.PluginLogger` (or IntelliJ's `Logger`) for all logging; never `System.out`.
+- All new files must include the standard Chromium Authors copyright header.
+- Zero-Formatting Policy: do not comment on indentation, spacing, or brace placement.
+- Categorize code suggestions with `[MUST-FIX]`, `[CONCERN]`, or `[NIT]` severity prefixes.