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};
 

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

@@ -23,8 +23,9 @@ static DB: LazyLock<Arc<db::DbPool>> = LazyLock::new(|| {
 /// create parent dirs, so the old hardcoded `data/task_queue.db` failed with
 /// a confusing error when started from a directory without `data/`, and a
 /// CWD-relative path is a footgun for systemd / cron deployments — `DATA_DIR`
-/// lets them pin the state anywhere.
-fn db_path() -> std::path::PathBuf {
+/// lets them pin the state anywhere. Also read by the startup config line, so
+/// the log says where the state actually landed.
+pub(crate) fn db_path() -> std::path::PathBuf {
     let dir = std::env::var("DATA_DIR").unwrap_or_else(|_| "data".to_string());
     let dir_path = std::path::Path::new(&dir);
     std::fs::create_dir_all(dir_path).expect("failed to create data directory");