Encrypt pages at rest with a key per person

Pages are sealed with AES-256-GCM. Each person's key is derived (HKDF) from a master key in the settings file plus their Authentik issuer and subject. Plain files from earlier versions are read and re-saved encrypted. Mako refuses to open a notebook it cannot decrypt rather than overwrite it.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

deploy/docker-compose.yml

@@ -14,4 +14,4 @@ services:
       MAKO_OIDC_CLIENT_SECRET: change-me
       # MAKO_ALLOWED: you@example.com   # optional: limit who may sign in
     volumes:
-      - ./config:/config       # mako.json (the signing secret) and data/ (your pages) live here
+      - ./config:/config       # mako.json (signing secret and note key; back it up apart from data/) and data/ live here