feat(log): survive a bare deployment and name what each line is about

P0 (foundation) + P1 (diagnostic depth) of the logging plan:

- main.rs initializes the timed builder with a default filter of
  `info,hyper_util=warn,reqwest=warn`. Without RUST_LOG nothing was logged at
  all (env_logger falls back to `error`), so `docker run --env-file .env` was
  silent, and the plain `init` had no timestamps.
- info-and-above lines stop printing user URLs (fetch/send failures, inline
  fetch, bsky's remux warnings). The full URL, the message text and the inline
  query move to `trace`, so a `debug` log can be handed to someone else.
- Lifecycle lines name the chat and the post: sent/failed/queued plus the
  total `ms`, the edit prompt, the channel forward, and every queue line
  (`chat=` + `[key=…]` + per-attempt `ms`, dead-letters included).
- Queue work is visible: `x-media`'s fetch line carries its duration (ugoira
  encode and HLS remux included), and the 300s sweep reports the pending count
  and how overdue the oldest task is — only when the queue is non-empty.
- URL workers are supervised like the queue workers: a panicking worker used
  to die silently and shrink the pool for the rest of the process.
- Degradations that still serve the user (cache/state write or read failures,
  a failed chat action) are `warn`, not `error`.

Verified against the scripted fake-API harness: unset RUST_LOG logs info with
timestamps, `debug` carries no user URL, `trace` does, a cache-hit send logs
`chat=111 in 5ms`, a failing send queues and dead-letters with chat+key, and
the sweep reports the pending retry.

crates/x-media/src/site/mod.rs

@@ -450,6 +450,9 @@ pub async fn fetch_once(url: &str) -> Result<Option<Fetched>, FetchError> {
 const MAX_FETCH_ATTEMPTS: u32 = 3;
 
 async fn fetch_with_attempts(url: &str, attempts: u32) -> Result<Option<Fetched>, FetchError> {
+    // Wall time of the whole fetch, retry backoff included: the ugoira encode
+    // and the HLS remux live inside it, so this is where a slow fetch shows.
+    let started = std::time::Instant::now();
     let Some(site) = find_site(url) else {
         // A registered-but-disabled site (pixiv without a token) is not an
         // unsupported link: report it, so the bot answers the user instead of
@@ -464,10 +467,11 @@ async fn fetch_with_attempts(url: &str, attempts: u32) -> Result<Option<Fetched>
             Ok(fetched) => {
                 // Per-request detail: debug only, keyed by the post id.
                 log::debug!(
-                    "fetched [key={}]: site {} returned {} media",
+                    "fetched [key={}]: site {} returned {} media in {}ms",
                     cache_key(url).unwrap_or_else(|| "?".into()),
                     fetched.site_name(),
-                    fetched.media.len()
+                    fetched.media.len(),
+                    started.elapsed().as_millis()
                 );
                 return Ok(Some(fetched));
             }