feat: deploy CouchDB on hf-pdocker-02 for Obsidian LiveSync (:5984)

Backs the Obsidian 'Second Brain' vault (private repo: git.hobbs.farm/jeremy/
second-brain) with self-hosted multi-device sync. LAN-only for now; no public
Traefik route yet.

- couchdb:3.4 pinned, Watchtower disabled, mem_limit 1g.
- Data on LOCAL disk (/var/lib/couchdb) -- CouchDB file locking breaks over
  NFSv3, same class as guacamole-db and semaphore-db.
- local.ini mounted READ-WRITE, deliberately: CouchDB 3.x writes runtime config
  back into the last-loaded ini, and with :ro it exits 1 and logs NOTHING --
  a silent crash-loop that is very hard to diagnose.
- CORS allows app://obsidian.md and capacitor://localhost (LiveSync desktop +
  mobile origins); a wildcard origin is not allowed alongside credentials.
- require_valid_user everywhere EXCEPT /_up, so the blackbox probe can health
  check it without credentials. Anonymous callers get 401 on all data.
- Admin credentials in Vaultwarden ('CouchDB - Obsidian LiveSync'); .env is
  gitignored, .env.example carries a placeholder.

Prometheus probe added (probe_success=1). Vault database: 'secondbrain'.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

compose/hf-pdocker-02/couchdb/local.ini

@@ -0,0 +1,30 @@
+; CouchDB config for Obsidian LiveSync.
+; Obsidian talks to CouchDB from an app:// origin, so CORS must allow it explicitly --
+; a wildcard origin is not permitted alongside credentials.
+
+[couchdb]
+single_node = true
+max_document_size = 50000000
+
+[chttpd]
+require_valid_user = true
+; ...but leave /_up open, so the Prometheus blackbox probe can health-check it
+; without credentials. Everything else still returns 401 to anonymous callers.
+require_valid_user_except_for_up = true
+max_http_request_size = 4294967296
+bind_address = 0.0.0.0
+
+[chttpd_auth]
+require_valid_user = true
+authentication_redirect = /_utils/session.html
+
+[httpd]
+WWW-Authenticate = Basic realm="couchdb"
+enable_cors = true
+
+[cors]
+credentials = true
+; Obsidian desktop is app://obsidian.md; mobile uses capacitor://localhost.
+origins = app://obsidian.md,capacitor://localhost,http://localhost
+methods = GET,PUT,POST,HEAD,DELETE
+headers = accept,authorization,content-type,origin,referer,x-csrf-token