feat(paths): OWLRY_SOCKET env var to override the IPC socket path

Adds a one-shot override before XDG_RUNTIME_DIR resolution so smoke
tests (and side-by-side daemon instances during dev) can run without
disturbing a production daemon listening on the default socket.

  - OWLRY_SOCKET=/tmp/foo.sock owlry -d
  - OWLRY_SOCKET=/tmp/foo.sock owlry providers

Test added (owlry_socket_env_overrides_xdg_runtime) verifying the
env var takes precedence and restoring the previous value so it
doesn't leak across other tests in the module.

Used to verify Phase 1 live behavior across all 13 provider entry
points — each returned expected results, including uuctl resolving
to real systemd unit names ('dbus' -> dbus-broker, at-spi-dbus-bus).
Issue #5 confirmed fixed end-to-end.

crates/owlry/src/paths.rs

@@ -157,10 +157,17 @@ pub fn system_data_dirs() -> Vec<PathBuf> {
 // Runtime files
 // =============================================================================
 
-/// IPC socket path: `$XDG_RUNTIME_DIR/owlry/owlry.sock`
+/// IPC socket path.
 ///
-/// Falls back to `/tmp` if `$XDG_RUNTIME_DIR` is not set.
+/// Resolution order:
+/// 1. `$OWLRY_SOCKET` — full path override (useful for tests and side-by-side
+///    daemon instances).
+/// 2. `$XDG_RUNTIME_DIR/owlry/owlry.sock` (the normal case).
+/// 3. `/tmp/owlry/owlry.sock` as a last-resort fallback.
 pub fn socket_path() -> PathBuf {
+    if let Ok(custom) = std::env::var("OWLRY_SOCKET") {
+        return PathBuf::from(custom);
+    }
     let runtime_dir = std::env::var("XDG_RUNTIME_DIR")
         .map(PathBuf::from)
         .unwrap_or_else(|_| PathBuf::from("/tmp"));
@@ -202,6 +209,22 @@ mod tests {
         }
     }
 
+    #[test]
+    fn owlry_socket_env_overrides_xdg_runtime() {
+        // SAFETY: tests in this binary do not run in parallel against the env.
+        // Save / restore so other tests in this module aren't affected.
+        let prev = std::env::var_os("OWLRY_SOCKET");
+        unsafe { std::env::set_var("OWLRY_SOCKET", "/tmp/owlry-smoke/foo.sock") };
+        assert_eq!(
+            socket_path(),
+            PathBuf::from("/tmp/owlry-smoke/foo.sock")
+        );
+        match prev {
+            Some(v) => unsafe { std::env::set_var("OWLRY_SOCKET", v) },
+            None => unsafe { std::env::remove_var("OWLRY_SOCKET") },
+        }
+    }
+
     #[test]
     fn test_frecency_in_data_dir() {
         if let Some(path) = frecency_file() {