Always on top: Add transparent support for on topped window (#44815)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request
Transparency support (best-effort)
> Not every window can be made transparent. Transparency is applied on a
best-effort basis and depends on how the target app/window is built and
rendered.

## When it may not work
* Windows with special rendering pipelines (e.g., certain
hardware-accelerated / compositor-managed surfaces).
* Some tool/popup/owned windows where the foreground window isn’t the
actual surface being drawn.

## How it works (high-level)
* Resolve the best target window (preferring the top-level/root window
over transient children).
* Apply Windows’ standard layered-window alpha mechanism (per-window
opacity) to adjust transparency.
* When unpinned, Restore the original opacity/state when possible.

If transparency doesn’t change, it means the window doesn’t support this
mechanism in its current configuration.
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## PR Checklist

- [X] Closes: 
#43278 
#42929
#28773

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issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed


https://github.com/user-attachments/assets/c97a87f2-3126-4e19-990f-8c684dbeb631

<img width="1119" height="426" alt="image"
src="https://github.com/user-attachments/assets/547671ee-81d3-4c94-8199-bf0c4b1b7760"
/>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/modules/alwaysontop/AlwaysOnTopModuleInterface/dllmain.cpp

@@ -105,17 +105,28 @@ public:
         }
     }
 
-    virtual bool on_hotkey(size_t /*hotkeyId*/) override
+    virtual bool on_hotkey(size_t hotkeyId) override
     {
         if (m_enabled)
         {
-            Logger::trace(L"AlwaysOnTop hotkey pressed");
+            Logger::trace(L"AlwaysOnTop hotkey pressed, id={}", hotkeyId);
             if (!is_process_running())
             {
                 Enable();
             }
 
-            SetEvent(m_hPinEvent);
+            if (hotkeyId == 0)
+            {
+                SetEvent(m_hPinEvent);
+            }
+            else if (hotkeyId == 1)
+            {
+                SetEvent(m_hIncreaseOpacityEvent);
+            }
+            else if (hotkeyId == 2)
+            {
+                SetEvent(m_hDecreaseOpacityEvent);
+            }
 
             return true;
         }
@@ -125,19 +136,48 @@ public:
 
     virtual size_t get_hotkeys(Hotkey* hotkeys, size_t buffer_size) override
     {
+        size_t count = 0;
+        
+        // Hotkey 0: Pin/Unpin (e.g., Win+Ctrl+T)
         if (m_hotkey.key)
         {
-            if (hotkeys && buffer_size >= 1)
+            if (hotkeys && buffer_size > count)
             {
-                hotkeys[0] = m_hotkey;
+                hotkeys[count] = m_hotkey;
+                Logger::trace(L"AlwaysOnTop hotkey[0]: win={}, ctrl={}, shift={}, alt={}, key={}", 
+                    m_hotkey.win, m_hotkey.ctrl, m_hotkey.shift, m_hotkey.alt, m_hotkey.key);
             }
+            count++;
+        }
 
-            return 1;
-        }
-        else
+        // Hotkey 1: Increase opacity (same modifiers + VK_OEM_PLUS '=')
+        if (m_hotkey.key)
         {
-            return 0;
+            if (hotkeys && buffer_size > count)
+            {
+                hotkeys[count] = m_hotkey;
+                hotkeys[count].key = VK_OEM_PLUS; // '=' key
+                Logger::trace(L"AlwaysOnTop hotkey[1] (increase opacity): win={}, ctrl={}, shift={}, alt={}, key={}", 
+                    hotkeys[count].win, hotkeys[count].ctrl, hotkeys[count].shift, hotkeys[count].alt, hotkeys[count].key);
+            }
+            count++;
         }
+
+        // Hotkey 2: Decrease opacity (same modifiers + VK_OEM_MINUS '-')
+        if (m_hotkey.key)
+        {
+            if (hotkeys && buffer_size > count)
+            {
+                hotkeys[count] = m_hotkey;
+                hotkeys[count].key = VK_OEM_MINUS; // '-' key
+                Logger::trace(L"AlwaysOnTop hotkey[2] (decrease opacity): win={}, ctrl={}, shift={}, alt={}, key={}", 
+                    hotkeys[count].win, hotkeys[count].ctrl, hotkeys[count].shift, hotkeys[count].alt, hotkeys[count].key);
+            }
+            count++;
+        }
+
+        Logger::trace(L"AlwaysOnTop get_hotkeys returning count={}", count);
+        return count;
     }
 
     // Enable the powertoy
@@ -175,6 +215,8 @@ public:
         app_key = NonLocalizable::ModuleKey;
         m_hPinEvent = CreateDefaultEvent(CommonSharedConstants::ALWAYS_ON_TOP_PIN_EVENT);
         m_hTerminateEvent = CreateDefaultEvent(CommonSharedConstants::ALWAYS_ON_TOP_TERMINATE_EVENT);
+        m_hIncreaseOpacityEvent = CreateDefaultEvent(CommonSharedConstants::ALWAYS_ON_TOP_INCREASE_OPACITY_EVENT);
+        m_hDecreaseOpacityEvent = CreateDefaultEvent(CommonSharedConstants::ALWAYS_ON_TOP_DECREASE_OPACITY_EVENT);
         init_settings();
     }
 
@@ -292,6 +334,8 @@ private:
     // Handle to event used to pin/unpin windows
     HANDLE m_hPinEvent;
     HANDLE m_hTerminateEvent;
+    HANDLE m_hIncreaseOpacityEvent;
+    HANDLE m_hDecreaseOpacityEvent;
 };
 
 extern "C" __declspec(dllexport) PowertoyModuleIface* __cdecl powertoy_create()