v0.3.6-perf

perf(v0.3.6): reduce binary size 17MB->14MB, memory by ~10MB

Binary optimizations (17MB -> 14MB, -18%):
- image: default-features=false, features=[png] (drops avif, exr, tiff, webp, gif, etc)
- alacritty_terminal: default-features=false (drops serde)
- wgpu: default-features=false per-platform (drops unused backends)
- winit: default-features=false, features=[rwh_06, x11, wayland, wayland-dlopen]
- arboard: default-features=false (drops image dep on Windows)
- resvg/usvg: default-features=false (drops gif, webp, memmap-fonts)
- tiny-skia: default-features=false, features=[std] (drops png-format)
- Drop unused x11 direct dep (winit handles it)
- LTO: thin -> fat for slightly better optimization

Memory optimizations (~10MB savings):
- Font atlas: 1536x1536 -> 1024x1024 (-5.4MB GPU)
- Scrollback default: 3000 -> 1000 lines (-4MB per tab)
- LTO: true -> fat