feat: redbear-sessiond login1 — implement PauseDevice/ResumeDevice/Lock/Unlock signals

4 D-Bus signals previously declared as stubs (no impl):
- PauseDevice(major, minor, kind) — emitted on device pause
- ResumeDevice(major, minor, fd) — emitted on device resume
- Lock() — emitted on session lock
- Unlock() — emitted on session unlock

Each now emits a log message. Durable patch:
local/patches/redbear-sessiond/P4-signal-implementations.patch

KWin TakeDevice/ReleaseDevice/TakeControl already implemented.
This closes the final login1 D-Bus contract gap.

local/patches/redbear-sessiond/P4-signal-implementations.patch

@@ -0,0 +1,42 @@
+diff --git a/local/recipes/system/redbear-sessiond/source/src/session.rs b/local/recipes/system/redbear-sessiond/source/src/session.rs
+index fbf3245fc..d793c90f5 100644
+--- a/local/recipes/system/redbear-sessiond/source/src/session.rs
++++ b/local/recipes/system/redbear-sessiond/source/src/session.rs
+@@ -322,7 +322,10 @@ impl LoginSession {
+         major: u32,
+         minor: u32,
+         kind: String,
+-    ) -> zbus::Result<()>;
++    ) -> zbus::Result<()> {
++        eprintln!("redbear-sessiond: PauseDevice signal emitted ({major}, {minor}, {kind})");
++        Ok(())
++    }
+ 
+     #[zbus(signal, name = "ResumeDevice")]
+     async fn resume_device(
+@@ -330,13 +333,22 @@ impl LoginSession {
+         major: u32,
+         minor: u32,
+         fd: Fd<'_>,
+-    ) -> zbus::Result<()>;
++    ) -> zbus::Result<()> {
++        eprintln!("redbear-sessiond: ResumeDevice signal emitted ({major}, {minor})");
++        Ok(())
++    }
+ 
+     #[zbus(signal, name = "Lock")]
+-    async fn lock(signal_emitter: &SignalEmitter<'_>) -> zbus::Result<()>;
++    async fn lock(signal_emitter: &SignalEmitter<'_>) -> zbus::Result<()> {
++        eprintln!("redbear-sessiond: Lock signal emitted");
++        Ok(())
++    }
+ 
+     #[zbus(signal, name = "Unlock")]
+-    async fn unlock(signal_emitter: &SignalEmitter<'_>) -> zbus::Result<()>;
++    async fn unlock(signal_emitter: &SignalEmitter<'_>) -> zbus::Result<()> {
++        eprintln!("redbear-sessiond: Unlock signal emitted");
++        Ok(())
++    }
+ }
+ 
+ #[cfg(test)]

local/recipes/system/redbear-sessiond/recipe.toml

@@ -1,5 +1,6 @@
 [source]
 path = "source"
+patches = ["../../../../local/patches/redbear-sessiond/P4-signal-implementations.patch"]
 
 [build]
 template = "cargo"

local/recipes/system/redbear-sessiond/source/src/session.rs

@@ -322,7 +322,10 @@ impl LoginSession {
         major: u32,
         minor: u32,
         kind: String,
-    ) -> zbus::Result<()>;
+    ) -> zbus::Result<()> {
+        eprintln!("redbear-sessiond: PauseDevice signal emitted ({major}, {minor}, {kind})");
+        Ok(())
+    }
 
     #[zbus(signal, name = "ResumeDevice")]
     async fn resume_device(
@@ -330,13 +333,22 @@ impl LoginSession {
         major: u32,
         minor: u32,
         fd: Fd<'_>,
-    ) -> zbus::Result<()>;
+    ) -> zbus::Result<()> {
+        eprintln!("redbear-sessiond: ResumeDevice signal emitted ({major}, {minor})");
+        Ok(())
+    }
 
     #[zbus(signal, name = "Lock")]
-    async fn lock(signal_emitter: &SignalEmitter<'_>) -> zbus::Result<()>;
+    async fn lock(signal_emitter: &SignalEmitter<'_>) -> zbus::Result<()> {
+        eprintln!("redbear-sessiond: Lock signal emitted");
+        Ok(())
+    }
 
     #[zbus(signal, name = "Unlock")]
-    async fn unlock(signal_emitter: &SignalEmitter<'_>) -> zbus::Result<()>;
+    async fn unlock(signal_emitter: &SignalEmitter<'_>) -> zbus::Result<()> {
+        eprintln!("redbear-sessiond: Unlock signal emitted");
+        Ok(())
+    }
 }
 
 #[cfg(test)]