feat: phase 5 — Tight decoder with zlib streams and sub-palettes

codec/tight.rs:
- Full Tight (encoding 7) decoder per ByteColorRFBRenderer.a() line 324
- Control byte: bottom 4 bits = zlib stream reset flags,
  top 4 bits = subencoding (0-15)
- Subencoding 8: solid fill (1-byte color)
- Subencoding 15: palette-indexed fill (selector + index)
- Subencodings 4-7: filtered data with optional 2-color palette
- Subencodings 10-13: reduced bit-depth packed (1/2/4 bpp)
- Subencodings 0-3: raw 8bpp data
- Data >= 12 bytes uses zlib compression with varint length
- 4 persistent zlib streams with reset-on-flag logic
- All 4 hardcoded sub-palettes ported as RGB332 indices:
  PALETTE_BW (2), PALETTE_GRAY4 (4), PALETTE_GRAY16 (16),
  PALETTE_COLOR16 (16 EGA-like colors)
- Bit-depth unpackers: 1bpp, 2bpp, 4bpp (MSB-first)
- 5 unit tests

Updated examples to request [7, 5, 1, 0, -250] (Tight preferred).
Tested against real OmniView: correct rendering with Tight encoding.
32 tests passing.

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

crates/ericrfb/src/session.rs

@@ -1,7 +1,7 @@
 use std::io::{BufReader, BufWriter};
 use std::net::TcpStream;
 
-use crate::codec::hextile;
+use crate::codec::{hextile, tight};
 use crate::framebuffer::Framebuffer;
 use crate::handshake::{self, Config, ServerInit};
 use crate::msg::{self, ServerMsg};
@@ -45,6 +45,7 @@ pub struct ActiveSession {
     pub reader: BufReader<TcpStream>,
     pub writer: BufWriter<TcpStream>,
     pub server_init: ServerInit,
+    zlib: tight::ZlibStreams,
 }
 
 impl ActiveSession {
@@ -57,6 +58,7 @@ impl ActiveSession {
             reader: raw.reader,
             writer: raw.writer,
             server_init: raw.server_init,
+            zlib: tight::ZlibStreams::new(),
         };
 
         // Tell server to send 8bpp RGB332 pixels
@@ -208,6 +210,18 @@ impl ActiveSession {
                         hdr.h,
                     )?;
                 }
+                7 => {
+                    // Tight
+                    tight::decode_tight(
+                        &mut self.reader,
+                        &mut self.framebuffer,
+                        &mut self.zlib,
+                        hdr.x,
+                        hdr.y,
+                        hdr.w,
+                        hdr.h,
+                    )?;
+                }
                 other => {
                     return Err(SessionError::UnsupportedEncoding(other));
                 }