chore(log): cap container log growth and echo the resolved config

P2 of the logging plan (the README recipe landed with the code change):

- `docker-compose.yml.example`: one `x-logging` anchor applied to all three
  services. json-file grows without limit by default, so a long-running bot
  and the proxy in front of it fill the disk; capped at 10m × 3 files.
- The startup `config:` line now reports what the process actually resolved —
  the state DB path (a mistyped `DATA_DIR` or a surprising CWD was invisible
  until it bit), both TTLs, the caption-quote setting (`off` rather than a bare
  `0`) and whether a proxy is configured. The proxy URL is never printed (it
  may embed credentials) and admin ids — chat identifiers — stay at `debug`.

Verified: `docker compose config -q` accepts the file, and a scripted fake-API
run shows `caption quote off` / `link cache TTL 3600s` under overrides,
`proxy=yes` with no credential in any line, and the ids at `debug` only.

docker-compose.yml.example

@@ -1,3 +1,12 @@
+# JSON-file logs grow without limit by default: a long-running bot (and the
+# proxy in front of it) will fill the disk. One cap, applied to every service
+# below via the anchor.
+x-logging: &default-logging
+  driver: json-file
+  options:
+    max-size: '10m'
+    max-file: '3'
+
 services:
   nginx-proxy:
     image: nginxproxy/nginx-proxy:1.11.6-alpine
@@ -13,6 +22,7 @@ services:
     labels:
       - 'com.github.nginx-proxy.nginx'
     container_name: nginx-proxy
+    logging: *default-logging
 
   acme-companion:
     image: nginxproxy/acme-companion
@@ -28,6 +38,7 @@ services:
     container_name: acme-companion
     depends_on:
       - nginx-proxy
+    logging: *default-logging
 
   tgxmb:
     image: yoursfunny/telegram-twitter-media-bot:latest
@@ -55,6 +66,7 @@ services:
     depends_on:
       - nginx-proxy
     container_name: tgxmb
+    logging: *default-logging
     # Webhook mode only: the bot listens on WEBHOOK_PORT; nginx-proxy shows
     # 502s while this is down, so surface it to the orchestrator.
     healthcheck: