chore(claude-seo): vendor as submodule pinned at v1.9.8-2-g4aa8f03

Replaces the unmanaged 6.5MB clone of AgriciDaniel/claude-seo at
claude.symlink/skills/claude-seo with a proper git submodule. The
gitlink is pinned at the SHA the working clone was sitting on so the
locally-tested behavior carries over. The local AGENTS.md customization
(~280 line rewrite) is preserved as a working-tree modification on this
machine; portable to other dotfiles checkouts only after forking.

Previous clone backed up to /tmp/claude-seo.bak.<ts>.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: htlin222

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "claude.symlink/skills/claude-seo"]
+	path = claude.symlink/skills/claude-seo
+	url = https://github.com/AgriciDaniel/claude-seo.git