feat(obsidian): add CouchDB stack for Obsidian LiveSync sync

Self-hosted sync backend for the Obsidian LiveSync plugin, following
https://blog.admin-intelligence.de/selbsthosting-von-obsidian-mit-couchdb-kostenlose-synchronisation-einrichten/.
local.ini.example carries the required chttpd/cors config; local.ini itself
is gitignored since CouchDB rewrites it in place (hashed admin password,
node uuid) on first start, so a tracked copy would never stay clean. The
config also has to be mounted read-write, not :ro: CouchDB's entrypoint
chowns everything under /opt/couchdb and aborts under set -e if that fails.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

obsidian/compose.yml

@@ -0,0 +1,36 @@
+services:
+  obsidian:
+    image: couchdb:latest
+    container_name: obsidian
+    environment:
+      TZ: ${TIMEZONE:-Europe/Amsterdam}
+      COUCHDB_USER: ${COUCHDB_USER}
+      COUCHDB_PASSWORD: ${COUCHDB_PASSWORD}
+    volumes:
+      - ../.data/obsidian:/opt/couchdb/data
+      - ./local.ini:/opt/couchdb/etc/local.d/local.ini
+    restart: always
+    healthcheck:
+      test: ["CMD-SHELL", "curl -sf -u \"$$COUCHDB_USER:$$COUCHDB_PASSWORD\" http://localhost:5984/_up || exit 1"]
+      interval: 5s
+      timeout: 5s
+      retries: 5
+    labels:
+      - "traefik.enable=true"
+      - "traefik.http.middlewares.obsidian-redirect-web-secure.redirectscheme.scheme=https"
+      - "traefik.http.routers.obsidian-web.middlewares=obsidian-redirect-web-secure"
+      - "traefik.http.routers.obsidian-web.rule=Host(`${TRAEFIK_HOST}`)"
+      - "traefik.http.routers.obsidian-web.entrypoints=web"
+      - "traefik.http.routers.obsidian-web-secure.rule=Host(`${TRAEFIK_HOST}`)"
+      - "traefik.http.routers.obsidian-web-secure.tls.certresolver=resolver"
+      - "traefik.http.routers.obsidian-web-secure.entrypoints=web-secure"
+      - "traefik.http.routers.obsidian-web-secure.middlewares=security-headers@file,no-index@file"
+      - "traefik.http.services.obsidian-web-secure.loadbalancer.server.port=5984"
+      - "traefik.docker.network=${NETWORK_NAME}"
+    networks:
+      - compose_network
+
+networks:
+  compose_network:
+    name: ${NETWORK_NAME}
+    external: true