Implement window-proc hooking path in HydraHook-ImGui sample

[coderabbitai]

Context

A TODO was added in PR #40 at line 1011 of samples/HydraHook-ImGui/dllmain.cpp indicating that the window-proc hooking path needs to be implemented.

Related PR: #40
Comment thread: #40 (comment)
Requested by: @nefarius

Description

The HookWindowProc function currently has incomplete implementation (guarded by #ifdef WNDPROC_HOOK). This issue tracks the work needed to implement a full, safe hook path for window procedure interception.

Implementation Requirements

The window-proc hooking path should:

1. Validate inputs: Check that the HWND and WNDPROC are valid before proceeding
2. Store original WNDPROC: Maintain a per-window map (e.g., originalWndProcMap) to store the original WNDPROC before replacing it
3. Install hook safely: Use SetWindowLongPtr/SetWindowSubclass to install the hook from HookWindowProc
4. Forward messages correctly: Use CallWindowProc (or CallWindowProcW) to forward messages to the saved original, preserving calling convention
5. Handle cleanup: On WM_NCDESTROY/WM_DESTROY, restore the original procedure
6. Thread safety: Guard map access and hook install/removal with a mutex/critical section (e.g., csHook) to avoid races and re-entrancy
7. Error handling: Add minimal error logging on failures so issues are visible

Current State

The WNDPROC_HOOK conditional block exists but needs the full implementation as described above to ensure overlay stability for input handling.