docs(examples): operator cookbook — six deployment recipes + premium-relay spec

Add ready-to-run .env + README recipes (personal, public-free, friends,
paid-access, paid-relay, community) and the premium-relay design overview,
with audit fixes to the config template and spec:

- Drop the inert INSTANCE_ID knob (config never read it) and document the real
  per-node id, which is derived from ADMIN_PUBLIC_URL.
- Warn that a placeholder PUBLIC_API_URL is rejected at boot in production
  (Nostr identity is on by default); soften the recipe "boots today" status.
- Remove dead template vars: BTC/LTC Core-RPC settings and the non-existent
  PUBLIC_EXPOSE_FEATURES (replaced with the real per-field landing switches).
- Mark ALTCHA_HMAC_KEY conditional in PoW-off recipes; blank placeholder
  payment creds so a recipe doesn't ship a key that fails validation.
- Fix premium-relay spec drift: the migration creates no premium_until index,
  disabled endpoints return 400/200 (not 404), and neutralize operator voice.

examples/personal/.env.example

@@ -7,9 +7,10 @@
 
 SERVER_HOST=127.0.0.1
 SERVER_PORT=8080
+# REQUIRED: replace with YOUR real https domain. The your-domain.example placeholder
+# is rejected at boot in production (Nostr identity is on by default).
 PUBLIC_API_URL=https://your-domain.example/api/v1
 ENVIRONMENT=production
-INSTANCE_ID=my-personal-node
 
 # Unix socket + peer auth (run the service as the DB-owning OS user) — no password.
 DATABASE_URL=postgresql:///smirk?host=/var/run/postgresql
@@ -19,6 +20,7 @@ JWT_SECRET=
 SEED_FINGERPRINT_PEPPER=
 REFRESH_TOKEN_PEPPER=
 IP_SALT=
+# ALTCHA_HMAC_KEY — only needed if you set FEATURE_POW=true (this recipe leaves PoW off).
 ALTCHA_HMAC_KEY=
 
 # No gates — it's just you.