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.

crates/xmedia-bot/src/handlers/mod.rs

@@ -15,6 +15,8 @@ mod urls;
 pub use callback::callback_query_handler;
 pub use commands::register_commands;
 pub use inline::inline_query_handler;
+/// The resolved `$DATA_DIR/task_queue.db` path, for the startup config line.
+pub(crate) use statics::db_path;
 pub use statics::{CHAT_STORE, CONFIG, LINK_CACHE, TASK_QUEUE};
 pub use urls::{start_url_workers, stop_url_workers};