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>

Cargo.lock

@@ -159,6 +159,7 @@ checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
 name = "ericrfb"
 version = "0.1.0"
 dependencies = [
+ "flate2",
  "png",
  "proptest",
  "thiserror",