feat: add Obsidian vault cookbook for knowledge base discovery

[kantord]

Summary

Add enwiro-cookbook-obsidian that discovers Obsidian vaults and surfaces them as recipes.

Motivation

Knowledge workers frequently switch between code projects and note-taking contexts. Obsidian vaults are self-contained directories that users interact with via terminal (git sync, grep, scripting) alongside the Obsidian app. Having vaults discoverable as enwiro environments lets users switch between code and notes workspaces seamlessly.

Implementation ideas

• Discover vaults by looking for directories containing a .obsidian/ subdirectory
• Configuration takes glob patterns for where to search (e.g., ~/Documents/*, ~/notes/*)
• Could also read Obsidian's own vault registry (~/.config/obsidian/obsidian.json on Linux) which lists all known vaults
• Recipe name could be the vault directory name
• Description field could show the vault path or number of notes
• cook returns the vault directory path