feat(theme-sync): persistent switch notification so slow switches read as progress

The "Applying theme — rebuilding…" toast used the default timeout, so it
vanished seconds into a multi-minute home-manager switch — leaving the
user with no signal and the impression the selection failed. Now it's
persistent (timeout 0) and all theme notifications share a synchronous
tag, so swaync REPLACES it in place with "Theme applied ✓" (or a critical
failure toast that persists) when the rebuild finishes.

notify() grew persistent/urgency/summary params. Honest indeterminate
feedback — HM exposes no percentage, so no fake progress bar.

Verified: py_compile clean; the full apply→switch→notify path runs end to
end (dummy NOMARCHY_REBUILD). The in-place replacement is visible only in
a real swaync session.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pkgs/nomarchy-theme-sync/nomarchy-theme-sync.py

@@ -59,10 +59,27 @@ def die(msg: str) -> "None":
     sys.exit(1)
 
 
-def notify(body: str) -> None:
-    if shutil.which("notify-send"):
-        subprocess.run(["notify-send", "-a", "Nomarchy", "Nomarchy", body],
-                       capture_output=True)
+# All Nomarchy theme notifications share this synchronous tag, so the
+# notification daemon (swaync) REPLACES the previous one in place instead
+# of stacking — the "rebuilding…" toast becomes the "applied ✓" toast.
+NOTIFY_SYNC_TAG = "nomarchy-theme-sync"
+
+
+def notify(body: str, summary: str = "Nomarchy", *,
+           persistent: bool = False, urgency: str = "normal") -> None:
+    """Desktop notification. persistent (timeout 0) keeps it up for the
+    whole rebuild so a slow switch never reads as a failed selection;
+    the success/failure call replaces it via the synchronous tag."""
+    if shutil.which("notify-send") is None:
+        return
+    subprocess.run(
+        ["notify-send", "-a", "Nomarchy",
+         "-u", urgency,
+         "-t", "0" if persistent else "5000",
+         "-h", f"string:x-canonical-private-synchronous:{NOTIFY_SYNC_TAG}",
+         summary, body],
+        capture_output=True,
+    )
 
 
 # ─── State management ─────────────────────────────────────────────────────
@@ -145,10 +162,13 @@ def run_switch() -> None:
         return
 
     log(f"rebuilding: {' '.join(argv)}")
-    notify("Applying theme — rebuilding the desktop…")
+    # Persistent (timeout 0): stays up for the whole rebuild — replaced
+    # in place by the success/failure notification below — so a multi-
+    # minute switch never looks like it silently failed.
+    notify("Applying theme — rebuilding the desktop…", persistent=True)
     result = subprocess.run(argv)  # stream output to the caller's terminal
     if result.returncode != 0:
-        notify("Theme rebuild FAILED — see terminal / journal")
+        notify("Theme rebuild FAILED — see terminal / journal", urgency="critical")
         die("rebuild failed (state file already updated; fix and re-run)")
     notify("Theme applied ✓")