docs: migrate Authentik (SSO keystone) to edge2 CT 105

- Authentik -> edge2 CT 105 (Postgres pg_dump/restore; SECRET_KEY carried verbatim; zero-downtime until ~2s cutover)
- Multi-block Caddy cutover: auth.echo6.co + notes.echo6.co outpost/forward_auth -> 100.64.0.36:9000
- runbook: add reboot tailscale-before-docker gotcha; clarify dnsmasq must NOT be repointed (points at Caddy host)
- source left stopped + intact on Contabo as cold rollback

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

vault/.obsidian/graph.json

@@ -0,0 +1,22 @@
+{
+  "collapse-filter": true,
+  "search": "",
+  "showTags": false,
+  "showAttachments": false,
+  "hideUnresolved": false,
+  "showOrphans": true,
+  "collapse-color-groups": true,
+  "colorGroups": [],
+  "collapse-display": true,
+  "showArrow": false,
+  "textFadeMultiplier": 0,
+  "nodeSizeMultiplier": 1,
+  "lineSizeMultiplier": 1,
+  "collapse-forces": true,
+  "centerStrength": 0.518713248970312,
+  "repelStrength": 10,
+  "linkStrength": 1,
+  "linkDistance": 250,
+  "scale": 1,
+  "close": false
+}