Add OpenWrt ipk packaging + split client/server binaries

OpenWrt package (deploy/openwrt/):
- build-ipk.sh: creates .ipk from pre-built binary (no SDK needed)
- Makefile: for OpenWrt SDK integration
- ProCD init script with UCI config
- Supports all architectures (x86_64, aarch64, mipsel, mips)

Split binaries for embedded (src/bin/):
- btest-client: client-only, no server/syslog/csv
- btest-server: server-only, no client
- release-small profile: opt-level=z + panic=abort

Sizes (compressed .tar.gz):
  Full btest:    ~1 MB
  btest-client:  ~500 KB (release-small)
  btest-server:  ~550 KB (release-small)

Install on OpenWrt:
  opkg install btest-rs_0.6.0-1_x86_64.ipk

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

Cargo.toml

@@ -16,6 +16,14 @@ path = "src/lib.rs"
 name = "btest"
 path = "src/main.rs"
 
+[[bin]]
+name = "btest-client"
+path = "src/bin/client_only.rs"
+
+[[bin]]
+name = "btest-server"
+path = "src/bin/server_only.rs"
+
 [dependencies]
 tokio = { version = "1", features = ["full"] }
 clap = { version = "4", features = ["derive"] }
@@ -38,3 +46,9 @@ opt-level = 3
 lto = true
 strip = true
 codegen-units = 1
+
+# Minimal size profile for embedded/OpenWrt targets
+[profile.release-small]
+inherits = "release"
+opt-level = "z"
+panic = "abort"