agent: finish tracing migration for hotkey logs

Follow-up to 184214b. The eprintln→tracing sweep surfaced 6 existing
log::* calls in the hotkey crate that were silent at runtime — the
workspace builds tracing-subscriber without the tracing-log feature, so
log:: events never reached the tracing pipeline.

Migrating direct rather than adding a LogTracer bridge: the repo is
already standardising on tracing, the bridge adds a second logger init
path with "already initialised" edge cases, and the bridge would
indiscriminately route all log records (including future third-party
chatter), not just these known sites.

Migrated (6 sites, 2 files):
- crates/hotkey/src/linux.rs (5) — read /dev/input error, device open
  debug, device-attached info, device-listener-ended warn, event-channel-
  closed warn
- crates/hotkey/src/stub.rs (1) — non-Linux no-op info

Also removed the now-unused log = "0.4" dependency from
crates/hotkey/Cargo.toml. magnotia_hotkey=info filter target was
already added to init_tracing in 184214b, so these events emit at the
default level immediately.

Verification:
- cargo fmt --all -- --check
- cargo check -p magnotia-hotkey — clean
- cargo check -p magnotia — clean
- rg 'log::|eprintln!' crates/hotkey/src/ src-tauri/src/commands/ crates/ai-formatting/src/ — zero hits

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/hotkey/Cargo.toml

@@ -8,7 +8,6 @@ description = "Wayland-compatible global hotkey listener for Magnotia — evdev
 magnotia-core = { path = "../core" }
 tokio = { version = "1", features = ["rt", "sync", "macros", "time"] }
 serde = { version = "1", features = ["derive"] }
-log = "0.4"
 tracing = "0.1"
 
 [target.'cfg(target_os = "linux")'.dependencies]

crates/hotkey/src/linux.rs

@@ -199,7 +199,7 @@ async fn scan_and_attach(
     let entries = match std::fs::read_dir(input_dir) {
         Ok(e) => e,
         Err(e) => {
-            log::error!("Cannot read /dev/input: {e}");
+            tracing::error!(error = %e, "cannot read /dev/input");
             return;
         }
     };
@@ -233,7 +233,7 @@ async fn try_attach_device(
     let device = match Device::open(path) {
         Ok(d) => d,
         Err(e) => {
-            log::debug!("Cannot open {}: {e}", path.display());
+            tracing::debug!(path = %path.display(), error = %e, "cannot open device");
             return false;
         }
     };
@@ -243,10 +243,10 @@ async fn try_attach_device(
     }
 
     let device_name = device.name().unwrap_or("unknown").to_string();
-    log::info!(
-        "Attached hotkey listener to: {} ({})",
-        device_name,
-        path.display()
+    tracing::info!(
+        device = %device_name,
+        path = %path.display(),
+        "attached hotkey listener"
     );
 
     tracked_set.insert(path.to_path_buf());
@@ -260,7 +260,11 @@ async fn try_attach_device(
 
     tokio::spawn(async move {
         if let Err(e) = device_listener(device, hotkey_rx, event_tx).await {
-            log::warn!("Device listener for {} ended: {e}", path_owned.display());
+            tracing::warn!(
+                path = %path_owned.display(),
+                error = %e,
+                "device listener ended"
+            );
         }
         // Remove from tracked set so hotplug can re-attach if reconnected
         tracked.lock().await.remove(&path_owned);
@@ -331,8 +335,8 @@ async fn device_listener(
                                             // shutdown. Log once and exit so
                                             // the listener doesn't spin
                                             // sending into a closed channel.
-                                            log::warn!(
-                                                "Hotkey event channel closed; \
+                                            tracing::warn!(
+                                                "hotkey event channel closed; \
                                                  listener for device exiting"
                                             );
                                             return Ok(());

crates/hotkey/src/stub.rs

@@ -19,7 +19,7 @@ pub struct EvdevHotkeyListener;
 
 impl EvdevHotkeyListener {
     pub fn start(_combo: HotkeyCombo, _event_tx: mpsc::Sender<HotkeyEvent>) -> Self {
-        log::info!("evdev hotkey listener is a no-op on this platform");
+        tracing::info!("evdev hotkey listener is a no-op on this platform");
         Self
     }