Fix single instance file forwarding on Windows

[wudi901]

Description

Fixes #605.

On Windows, when "Allow only one Snapmaker Orca instance" is enabled and the app is already running, launching the executable again with a model file (double-clicking an STL/3MF, or exporting from Fusion) terminated the second process without forwarding the file path.

Root cause: EnumWindowsProc in src/slic3r/GUI/InstanceCheck.cpp searched for a main window whose title contains Snapmaker_Orca (underscore), but the Windows main frame title is set in Plater::priv::set_project_name as "<project> - Snapmaker Orca" (space). The primary window was therefore never found, WM_COPYDATA was never delivered, and the command line was dropped silently.

Fix: match the title against SLIC3R_APP_NAME instead of a hardcoded string, so the window search stays in sync with the branded title.

Screenshots/Recordings/Graphs

Not applicable (no UI change).

Tests

• No automated coverage exists for the Windows single-instance IPC path; automated tests not run for this change.
• Manual verification on Windows:
  1. Enable "Allow only one Snapmaker Orca instance" and launch the app.
  2. Double-click an STL/3MF file (or export from Fusion) while the app is running.
  3. The running instance is brought to the front and loads the model; the log shows win enum - found correct instance.

[zhangzhend0ng]

Review: impact scope & regression risk — non-blocking findings

The fix itself is verified correct: the title producer Plater.cpp:16407 sets " - Snapmaker Orca" (space) while the old matcher searched for the underscore variant; the second-instance lifecycle is unchanged (send_message's return value is ignored at InstanceCheck.cpp:361 — the wxSingleInstanceChecker mutex alone decides termination); and the WM_COPYDATA receiver (GUI_App.cpp:834) was already registered, so no new attack surface. Impact is limited to users with app/single_instance=true (default false).

Non-blocking findings in priority order (two more anchored inline on the changed line):

1. Plater.cpp:16407 — title producer still hardcoded (one line, this PR or follow-up). The matcher now derives from SLIC3R_APP_NAME while the producer is a literal; they coincide today, and renaming either side resurrects this exact bug. Suggest SetTitle(m_project_name + " - " + SLIC3R_APP_NAME).

2. MainFrame.cpp:240 — empty title during early startup (record only). The main frame is constructed with an empty title and only gets the app name via Plater::priv::set_project_name, so during that brief startup window a second instance still cannot forward. Pre-existing behavior, unchanged by this PR.

3. Root-cure follow-up: sync upstream's approach. Upstream SoftFever/OrcaSlicer removed title matching entirely — their EnumWindowsProc matches class wxWindowNR + presence of Instance_Hash_Minor/Major window props + hash equality (props are set only on the real main frame). That decouples instance detection from branding strings and also eliminates the Settings-dialog over-match noted inline.

[zhangzhend0ng]

Non-blocking, but worth one line in this PR: now that the window is actually found, the unconditional ShowWindow(hwnd, SW_SHOWMAXIMIZED) further down in this callback (~line 126) becomes live behavior: every second launch that forwards a file force-maximizes the running instance's window, even if the user had it restored or snapped. Upstream OrcaSlicer deliberately softened this:

// Do not alter the window state when opening a file in the existing instance.
// A minimized window still needs restoring before it can receive focus.
if (IsIconic(hwnd))
    ShowWindow(hwnd, SW_RESTORE);
SetForegroundWindow(hwnd);

Suggest adopting the same (SetForegroundWindow stays as-is).

[zhangzhend0ng]

Non-blocking, record: with the substring now matching, any top-level wxWindowNR window whose title contains the app name gets probed — including our own Settings dialog (SLIC3R_APP_NAME + " - " + _L("Settings"), MainFrame.cpp:4309). The instance-hash guard handles it correctly (GetProp returns NULL → hash 0 ≠ real instance hash → "win enum - found wrong instance" debug log and enumeration continues), so this is log noise only, no functional risk. It disappears if a follow-up adopts upstream's GetProp-based matching (no title string involved at all).

[wudi901]

Addressed both actionable findings in 2b83e3b:

• EnumWindowsProc now restores the window only when minimized (IsIconic + SW_RESTORE) instead of unconditionally maximizing it, matching upstream behavior.
• Plater::priv::set_project_name now builds the Windows title from SLIC3R_APP_NAME, so the producer and matcher share the same branding constant.

Thanks for the review! The Instance_Hash_*-based matching looks like the right follow-up as you suggested.