feat: phase 0+1 — workspace scaffold and protocol primitives

Phase 0: Cargo workspace with ericrfb (lib) and ericrfb-proxy (bin)
crates, .envrc for RUST_LOG, workspace dependency pins.

Phase 1: ericrfb/src/proto.rs implements all wire primitives:
- read/write helpers matching h.java (u8, i8, u16-BE, i16-BE, i32-BE)
- varint reader/writer matching aw.int() (1-3 bytes, Tight lengths)
- modified-UTF-8 string reader matching h.byte()
- RectHeader { x: u16, y: u16, w: u16, h: u16, encoding: i32 }
- RGB332 → RGBA compile-time LUT (256 entries)

20 tests including proptest varint roundtrip over [0, 2^22).

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

crates/ericrfb-proxy/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "ericrfb-proxy"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+ericrfb = { path = "../ericrfb" }
+tokio.workspace = true
+axum.workspace = true
+tracing.workspace = true
+tracing-subscriber.workspace = true
+anyhow.workspace = true

crates/ericrfb-proxy/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}