fix: send SetPixelFormat to request 8bpp RGB332

The OmniView defaults to 16bpp when no SetPixelFormat is sent.
The Java applet sends SetPixelFormat (msg type 0) at
ByteColorRFBRenderer.new() line 76 to request 8bpp RGB332
(bpp=8, depth=8, true_color, red_max=7, green_max=7, blue_max=3,
shifts 0/3/6). Without this, pixel data arrives as 16bpp pairs
that produce green stripe artifacts when interpreted as 8bpp.

Verified: snapshot now matches the reference screenshot from
http://10.3.0.130/screenshot.jpg (dark screen with "Free" label).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/ericrfb/src/session.rs

@@ -58,6 +58,9 @@ impl ActiveSession {
             server_init: raw.server_init,
         };
 
+        // Tell server to send 8bpp RGB332 pixels
+        msg::write_set_pixel_format_rgb332(&mut session.writer)?;
+
         // Send SetEncodings
         msg::write_set_encodings(&mut session.writer, encodings)?;