feat: add PyInstaller spec and GitHub Actions release workflow

Enables cross-platform builds for Windows and macOS. Adds _bin() helper
to resolve bundled ffmpeg in frozen builds, and configures ctypes library
path for bundled libmpv.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

8cut.spec

@@ -0,0 +1,143 @@
+# -*- mode: python ; coding: utf-8 -*-
+"""PyInstaller spec for 8-cut.
+
+Usage:
+    pyinstaller 8cut.spec
+
+Platform-specific notes:
+    Windows: place libmpv-2.dll, ffmpeg.exe, ffprobe.exe next to main.py
+             before building, or set FFMPEG_DIR / MPV_DIR env vars.
+    macOS:   place libmpv.2.dylib, ffmpeg, ffprobe next to main.py
+             before building, or set FFMPEG_DIR / MPV_DIR env vars.
+    Linux:   system libmpv and ffmpeg are used from PATH (not bundled).
+"""
+
+import os
+import platform
+import sys
+from pathlib import Path
+
+block_cipher = None
+system = platform.system()
+
+# ---------- paths ----------------------------------------------------------
+
+base = Path(SPECPATH)
+ffmpeg_dir = Path(os.environ.get("FFMPEG_DIR", base))
+mpv_dir = Path(os.environ.get("MPV_DIR", base))
+
+# ---------- data files -----------------------------------------------------
+
+datas = []
+
+# YOLOv8 model (optional — large, skip if missing)
+yolo = base / "yolov8n.pt"
+if yolo.exists():
+    datas.append((str(yolo), "."))
+
+# ---------- native binaries ------------------------------------------------
+
+binaries = []
+
+if system == "Windows":
+    for name in ("libmpv-2.dll",):
+        p = mpv_dir / name
+        if p.exists():
+            binaries.append((str(p), "."))
+    for name in ("ffmpeg.exe", "ffprobe.exe"):
+        p = ffmpeg_dir / name
+        if p.exists():
+            binaries.append((str(p), "."))
+
+elif system == "Darwin":
+    for name in ("libmpv.2.dylib", "libmpv.dylib"):
+        p = mpv_dir / name
+        if p.exists():
+            binaries.append((str(p), "."))
+            break
+    for name in ("ffmpeg", "ffprobe"):
+        p = ffmpeg_dir / name
+        if p.exists():
+            binaries.append((str(p), "."))
+
+# ---------- analysis -------------------------------------------------------
+
+a = Analysis(
+    [str(base / "main.py")],
+    pathex=[str(base)],
+    binaries=binaries,
+    datas=datas,
+    hiddenimports=[
+        "mpv",
+        "PyQt6.QtOpenGL",
+        "PyQt6.QtOpenGLWidgets",
+    ],
+    hookspath=[],
+    hooksconfig={},
+    runtime_hooks=[],
+    excludes=[
+        # ultralytics is optional and huge — exclude from frozen build
+        "ultralytics",
+        "torch",
+        "torchvision",
+        "onnxruntime",
+        "opencv-python",
+        # test / dev
+        "pytest",
+        "hypothesis",
+    ],
+    noarchive=False,
+    cipher=block_cipher,
+)
+
+pyz = PYZ(a.pure, cipher=block_cipher)
+
+# ---------- executable -----------------------------------------------------
+
+exe_kwargs = dict(
+    pyz=pyz,
+    a=a,
+    name="8cut",
+    debug=False,
+    bootloader_ignore_signals=False,
+    strip=False,
+    upx=True,
+    console=False,  # GUI app
+)
+
+if system == "Darwin":
+    exe_kwargs["icon"] = str(base / "assets" / "logo.png")
+elif system == "Windows":
+    ico = base / "assets" / "logo.ico"
+    if ico.exists():
+        exe_kwargs["icon"] = str(ico)
+
+exe = EXE(**exe_kwargs)
+
+# ---------- collect --------------------------------------------------------
+
+coll = COLLECT(
+    exe,
+    a.binaries,
+    a.datas,
+    strip=False,
+    upx=True,
+    upx_exclude=[],
+    name="8cut",
+)
+
+# ---------- macOS .app bundle (only on Darwin) -----------------------------
+
+if system == "Darwin":
+    app = BUNDLE(
+        coll,
+        name="8cut.app",
+        icon=str(base / "assets" / "logo.png"),
+        bundle_identifier="com.8cut.app",
+        info_plist={
+            "CFBundleDisplayName": "8cut",
+            "CFBundleShortVersionString": "1.0.0",
+            "NSHighResolutionCapable": True,
+            "LSMinimumSystemVersion": "11.0",
+        },
+    )