Reduce panel allocations and fix transient surface leaks (#19)

Repeated panel updates rebuilt unchanged controls and SVG artwork, cloned composition data, and kept unused workspace icon resources. This reuses controls when their layout stays the same, bounds the SVG cache, removes temporary layout allocations, and releases icon resources when apps close or the workspace style changes.

Rapidly closing a modal could also leave a native surface behind when its asynchronous creation finished after the close. Late openings now get destroyed when their owner is gone. Ferese uses the published `ferese-v0.1.2` Iced/libcosmic fixes so a temporary software buffer/viewport size mismatch retries the frame instead of crashing.

Two runs per version of the same workspace/overview/reload workload measured **26% fewer allocated bytes and 23% fewer allocation calls**. A separate 1,800-cycle notification/modal stress run retained about **40 MiB less shell memory**, including shared-buffer retention falling from 28.2 MiB to 272 KiB. These are measured workload results, not an overall desktop speedup claim.

Validation:
- 1,350 workspace tests passed, including GPU Settings text rendering (50 optional tests ignored); formatting and Clippy passed.
- Native continuous/island panel tests passed rapid notification resizing, modal cancellation, and live material/input-region changes.
- A Wayland lifetime trace confirmed all 280 created modal surfaces were destroyed; longer DHAT traces and Intel GPU memory measurements were checked separately.
- All installation binaries rebuilt and the installation bundle passed inventory and checksum verification.

scripts/tests/test_shell_motion_isolated.py

@@ -89,10 +89,15 @@ class ShellMotionTest(unittest.TestCase):
                                       env=ipc_environment(env), text=True, capture_output=True, timeout=5, check=check)
 
             def layer_surface(namespace):
-                matches = list(re.finditer(r'get_layer_surface\([^\n]*?wl_surface[@#](\d+)[^\n]*"' + namespace + '"', log_path.read_text()))
+                matches = layer_surfaces(namespace)
                 # Wayland object IDs can be reused after destruction. Restrict
                 # assertions to this surface's lifetime in the trace.
-                return (matches[-1].group(1), matches[-1].start()) if matches else None
+                return matches[-1] if matches else None
+
+            def layer_surfaces(namespace):
+                return [(match.group(1), match.start()) for match in re.finditer(
+                    r'get_layer_surface\([^\n]*?wl_surface[@#](\d+)[^\n]*"' + namespace + '"',
+                    log_path.read_text())]
 
             def frames(surface):
                 identity, start = surface
@@ -200,6 +205,48 @@ class ShellMotionTest(unittest.TestCase):
                     self.assertNotIn("panicked at", log_path.read_text())
                     print(f"Modal: {frames(modal)} callbacks; interrupted opening closed and destroyed", flush=True)
 
+                    # A toast can resize or start closing before its previous
+                    # software buffer has caught up with the new viewport.
+                    for index in range(40):
+                        reply = dbus("Notify", "Ferese motion test", "0", "", "Rapid toast",
+                                     "Short body", "[]", "{}", "0").stdout
+                        notice = re.search(r'uint32 (\d+)', reply).group(1)
+                        if index % 2 == 0:
+                            dbus("Notify", "Ferese motion test", notice, "", "Updated toast",
+                                 "A longer notification body that wraps over several lines. " * 6,
+                                 "[]", "{}", "0")
+                        dbus("CloseNotification", notice)
+                        time.sleep(.015)
+                    time.sleep(.5)
+                    self.assertIsNone(compositor.poll(), log_path.read_text()[-8000:])
+                    self.assertEqual(dbus("GetServerInformation", check=False).returncode, 0)
+                    self.assertNotIn("panicked at", log_path.read_text())
+                    print("Toast: 40 rapid open/update/close cycles completed", flush=True)
+
+                    for _ in range(40):
+                        subprocess.run([str(ctl), "toggle-keybinding-guide"],
+                                       env=ipc_environment(env), check=True, capture_output=True)
+                        time.sleep(.03)
+                        subprocess.run([str(ctl), "toggle-keybinding-guide"],
+                                       env=ipc_environment(env), check=True, capture_output=True)
+                        time.sleep(.06)
+                    # A final toggle may leave the owned modal closing. Let
+                    # that motion finish before deciding whether a live modal
+                    # needs another toggle; toggling during closing reopens it.
+                    deadline = time.monotonic() + 5
+                    while True:
+                        remaining = [surface for surface in layer_surfaces("ferese-system-modal")
+                                     if not destroyed(surface)]
+                        if not remaining or time.monotonic() >= deadline:
+                            break
+                        time.sleep(.05)
+                    self.assertLessEqual(len(remaining), 1, "cancelled modals retained native surfaces")
+                    if remaining:
+                        subprocess.run([str(ctl), "toggle-keybinding-guide"],
+                                       env=ipc_environment(env), check=True, capture_output=True)
+                        wait_for(lambda: destroyed(remaining[0]))
+                    print("Modal: rapid toggles released all native surfaces", flush=True)
+
                     if bar_layout == "islands":
                         for layout_name, expected_count in [("continuous", 1), ("islands", None)]:
                             config_file.write_text('animations { speed 0.5; }\nstatus { keybinding-guide #false; }\n' + panel_config(layout_name))