* fix(linux): defer buffer_scale until the first frame is presented
The video plane's wl_egl_window starts as a 1x1 placeholder. When playback starts, SetRect() sends wl_surface.set_buffer_scale(2) and resizes the window, but mesa commits the EGL surface's pre-allocated 1x1 back buffer on the first eglSwapBuffers. A 1x1 buffer is not an integer multiple of scale 2, so the compositor raises WL_SURFACE_ERROR_INVALID_SIZE, tears down the Wayland connection and plezy exits (issue #1872). At display scale 100% the same 1x1 buffer is legal, which is why that workaround worked.
Defer sending the new scale until after the first commit: the first buffer is 1x1 at scale 1 (always legal), then the scale change lands on the wire and applies to the next commit, whose buffer mesa allocates at the resized window size. The one-frame 1x1 flash is mpv's black first frame - imperceptible.
* fix(linux): gate buffer_scale on a first-frame latch, reset state on destroy
Address review: buffer_attached_ cannot represent "first frame
presented" - DetachBuffer() clears it while the committed scale stays
on the wire, leaving a crash path (present at scale 2, detach, move to
a scale-1 display, then a swap commits a scale-1 buffer while scale 2
is still active).
Replace it with first_frame_presented_, set once a frame has been
presented and cleared only when the wl_surface is torn down, so scale
changes queue even with no buffer attached. Reset scale_sent_ to 1 in
Destroy() too: a freshly created wl_surface starts at scale 1, and a
stale value would suppress the first scale request after recreation.
