feat(obsidian-markdown): add skill

Generated-by: Claude Opus 5.5

README.md

@@ -45,6 +45,9 @@ Code](https://code.claude.com/docs/en/skills) and
   with live links, quoted and dated.
 - [ibis-design](ibis-design/SKILL.md) — search a design space:
   issues, positions, and arguments.
+- [obsidian-markdown](obsidian-markdown/SKILL.md) — the workspace is
+  an Obsidian vault: one line per paragraph, relative links, no file
+  symlinks you expect Obsidian to show.
 
 ## at the terminal