fix: use ~/m3ta-brain instead of hardcoded server path

Vault location is now portable: ~/m3ta-brain resolves per-machine.
On m3-hermes: /var/lib/hermes/m3ta-brain
On desktop: /home/m3tam3re/m3ta-brain
On work laptop: /home/sascha.koenig/m3ta-brain

Updated in SKILL.md (5 occurrences) and references/vault-map.md (1).

skills/m3ta-brain/references/vault-map.md

@@ -107,7 +107,7 @@ python3 -c "
 import os, re
 from collections import defaultdict
 
-VAULT = '/var/lib/hermes/workspace/m3ta-brain'
+VAULT = os.path.expanduser('~/m3ta-brain')
 md_files = []
 for root, dirs, files in os.walk(VAULT):
     if '.git' in root or '.obsidian' in root: continue