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/xmedia-bot/src/send/post_send.rs

@@ -257,8 +257,9 @@ pub(crate) async fn post_send_actions(ctx: &AppContext<'_>, task: &Task, message
         match prompt {
             Ok(prompt_id) => {
                 log::info!(
-                    "edit-before-forward prompt {prompt_id} opened for {} message(s)",
-                    message_ids.len()
+                    "edit-before-forward prompt {prompt_id} opened for {} message(s) [key={}] chat={chat_id}",
+                    message_ids.len(),
+                    log_key(&source_url)
                 );
                 let source_url = source_url.clone();
                 ctx.chat_store
@@ -283,8 +284,9 @@ pub(crate) async fn post_send_actions(ctx: &AppContext<'_>, task: &Task, message
 
     if let Some(channel_id) = forward_channel_id {
         log::info!(
-            "forwarding {} message(s) to channel {channel_id}",
-            message_ids.len()
+            "forwarding {} message(s) to channel {channel_id} from chat {chat_id} [key={}]",
+            message_ids.len(),
+            log_key(&source_url)
         );
         let forward_task = Task::ForwardMessages {
             from_chat_id: chat_id,