obsidian: self-hosted vault sync via CouchDB on jupiter

Adds services/dev/obsidian-livesync.nix — CouchDB 3 from the native
nixpkgs module, tuned as the backend for the Self-hosted LiveSync plugin
— and publishes it as notes.mgaction.town through neptun.

It goes out over the public reverse proxy rather than staying on the LAN
because Obsidian's mobile apps refuse cleartext HTTP and *.jupiter.sol
cannot hold a publicly trusted cert. That makes the hardening load-bearing
rather than decorative:

  - require_valid_user in both [chttpd] and [chttpd_auth], so nothing
    answers unauthenticated on the open internet;
  - neptun's vhost matches on CouchDB's own naming rule (system endpoints
    all begin with `_`, user databases never can), so Fauxton, /_all_dbs
    and /_node/_local/_config — which rewrites the server config given
    admin credentials — 404 at the proxy while any number of per-vault
    databases pass. Verified against both sets of paths with caddy run
    against a stub backend;
  - the plugin's own E2EE carries the actual confidentiality: jupiter only
    ever stores ciphertext. Its passphrase is deliberately NOT in sops —
    it never leaves the clients, and pairing it with the server credential
    would defeat the point.

flush_interval -1 is required, not tuning: replication rides a continuous
_changes feed that caddy would otherwise buffer into a stall.

Storage sits on the array with RequiresMountsFor, since a CouchDB that
starts without /mnt/data would create an empty database on the eMMC and
LiveSync would replicate that emptiness back to every client. Logs go to
journald rather than the unrotated /var/log/couchdb.log, for the same
29G-eMMC reasons as the rest of jupiter.

The admin password reaches CouchDB as an [admins] ini fragment via
extraConfigFiles; services.couchdb.adminPass would have rendered it into
the world-readable store.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TLN5nkLBtCciD3ZnUwtw2b

secrets/jupiter.yaml

@@ -15,6 +15,7 @@ sabnzbd_nzb_key: ENC[AES256_GCM,data:DNVenqhJ7wf5Ng0XRA1gJN95e+90e6D9NImOSHJv/Us
 sabnzbd_eweka_username: ENC[AES256_GCM,data:eLsTZoM8T8fAlGaXWlDaoQ==,iv:eawyGhN7+d6UfBIbI3y1qgq+MYBGrXP6VfAkSOK6llA=,tag:ELOfQGHU5NOxZFhKOKf8LA==,type:str]
 sabnzbd_eweka_password: ENC[AES256_GCM,data:Mt3ZHAe2wzacCQq3x9Uy8WxjrVNad1SmU6sl8ZgrkMLymfq2eP4JzO/uPdD33A==,iv:PnFT95Zxqz4QBpPF5PRloKpoa15AU7Ef/Owwy+iDotw=,tag:/uRX00RzHLJN3gws5Qz8SA==,type:str]
 gitea_hermes_webhook_secret: ENC[AES256_GCM,data:Q8e+mj05MJI7CEJwRonpOmQphAZ0CfnZFoGxrDSSiyHoH3BNhqBU5gBmzuu+6NK9OS33kN+JnFvrwCeEzVxooA==,iv:mdsKOMD5B0Jzh1YRmRh71P8Io9RFtI6aqAky5x+WxOQ=,tag:v3LKz5a8ayl7WAzIPbwj6Q==,type:str]
+couchdb_admin_password: ENC[AES256_GCM,data:QHkCFUwLbQdd5yKETI5qAz4CkEfsPcl2iCU8F9mX3PA=,iv:2dPNKjjoXEgm7wfC6MlhQTMvAXSNDtaXnjWl2ldl4fk=,tag:1ZltqH94Q5/6GbXAnaIgdg==,type:str]
 sops:
     age:
         - enc: |
@@ -35,7 +36,7 @@ sops:
             CzjSDQZTcseEXZNwuzZcfB5Mvq0BQvjOj7lGuxzuE4qwWkdJWGfVLQ==
             -----END AGE ENCRYPTED FILE-----
           recipient: age1zak7glavmg4026p2389fyqe769vqm4jrryknuqckgqq4merz5f7q44rkkt
-    lastmodified: "2026-08-23T03:16:52Z"
-    mac: ENC[AES256_GCM,data:uQcOxORIWugK43LpQLI7JEjH6oGooseKCQQt0d+n43i7o23JGdUN5Wy/iD7GqmtVVZod02gl1ohEXV+kpvgetFpAO5NZu76HUVPFgaLOx+2LjrR1pNpC+52Iqlx52uypwby9eDvnC01jLFHu2l13NGBrLM3JQGmEXF57phzM/Q4=,iv:H7o3gdx/1GmZ1FRm7z97TNmiVpm6YFCEk0Puw4ZETDs=,tag:bsz3bcK2z3szrwpo55bSzQ==,type:str]
+    lastmodified: "2026-08-25T20:39:37Z"
+    mac: ENC[AES256_GCM,data:Z59BCw8gETfddXqul4LXrq6V3LBJA1itF7A1VNUERwK4NfaUGwWUhbl9h7YF/srzgtg9yGjbFB/f5kwmT3k/TWTG+C0M/4KOyTVs4y5UvB9gI4g8awYbtnFDPRAcqqcxoMD0sgapgVcNh48KWv76ndF6UGn+QfWn9eF4KBP+ZzQ=,iv:57myu1aTMMSLTz+1ldwxdusnzh8cyPwrLiEIx3rLS9w=,tag:isthpdOydD4ZNoFZyflViw==,type:str]
     unencrypted_suffix: _unencrypted
     version: 3.13.3