DeadAir in the page: a switch per show, one beside the speed, and the time saved (#172)

A DeadAir switch in each show's settings, and the same switch beside
the speed for the show that is playing, drawn as a waveform with its gap
closed up, outlined when off and solid when on, with aria-pressed. A
file the server gives a copy for plays from /media/{id}/deadair. An
episode's line says how much shorter it is, and Settings says how much
DeadAir has saved you.

Turning it on or off mid-episode saves the place with a request it waits
for, not a beacon, then asks for the entry again from the new
GET /api/entries/{feed}/{guid}, whose position is in the clock of the
version it now plays, and carries on there. A copy not made yet plays
from the next time. Turning a show on wakes the copy maker, so the copy
is there in seconds rather than at its next pass.

The browser test plays a real MP3 with long silences, quiet.mp3, from a
show it adds and removes itself.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -153,6 +153,9 @@ pub struct Ctx {
     // own, and a change in flight here can still store over theirs; take the copy from the
     // database rather than memory if that ever happens.
     pub cfg_write: tokio::sync::Mutex<()>,
+    /// Wakes DeadAir's maker when a show is turned on, so its copies start at once instead of
+    /// at the next pass (#171).
+    pub deadair: tokio::sync::Notify,
 }
 
 /// A copy of the config to change, holding off every other change until `store_cfg` keeps it.
@@ -345,6 +348,7 @@ async fn main() -> Result<()> {
         detach_torrents: is_daemon,
         retry: Default::default(),
         cfg_write: Default::default(),
+        deadair: Default::default(),
     });
 
     let result = match cli.command {
@@ -2458,6 +2462,7 @@ mod tests {
             detach_torrents: false,
             retry: Default::default(),
             cfg_write: Default::default(),
+            deadair: Default::default(),
         }
     }