Use @AGENTS.md import in CLAUDE.md instead of symlink

Per review feedback on the sibling flow-ai-tools PR (#33): replace
the CLAUDE.md → AGENTS.md symlink with a plain-text CLAUDE.md whose
single line is the @AGENTS.md import directive.

Claude Code treats @filename as an explicit import that guarantees
the referenced file is loaded, whereas symlink following is
heuristic. The @import approach also avoids Windows / non-Unix
filesystem compatibility issues where symlinks degrade to plain-
text files containing the target path.

Author: Aliserag

CLAUDE.md

@@ -0,0 +1 @@
+@AGENTS.md