Declare proprietary licensing and enforce permissive-only dependencies

Continuum is intended to be sold, so every dependency has to permit
distribution in closed-source commercial software. This crate carried
`license = "UNLICENSED"`, which is not valid SPDX and made `cargo deny`
fail outright; `LicenseRef-Proprietary` with `publish = false` is what
marks it first-party instead.

The note in deny.toml is the part that earns its keep: `src/go2rtc.rs`
spawns go2rtc from PATH and expects the operator to have installed it, so
we currently distribute nothing. go2rtc shells out to ffmpeg, and ffmpeg
is LGPL-2.1+ only when built without `--enable-gpl` - most prebuilt
binaries are GPL builds because they bundle x264. If we ever ship either
binary, those build flags become our problem.

Policy and full audit: continuum-common's docs/LICENSES.md.

Cargo.toml

@@ -3,7 +3,10 @@ name = "continuum-proxy"
 version = "0.1.0"
 edition = "2024"
 description = "Continuum edge gateway daemon - runs on-site, bridges printers to the cloud control plane"
-license = "UNLICENSED"
+# Proprietary: deliberately not an SPDX id, so cargo-deny treats it as
+# first-party. See docs/LICENSES.md in continuum-common.
+license = "LicenseRef-Proprietary"
+publish = false
 
 [lib]
 name = "continuum_proxy"
@@ -29,6 +32,8 @@ path = "examples/auto_connect_bambu.rs"
 name = "bambu_commands_demo"
 path = "examples/bambu_commands_demo.rs"
 
+
+
 [dependencies]
 # Real printer protocol clients (MQTT for Bambu, HTTP for PrusaLink/
 # Moonraker, FTPS for gcode transfer) go here once you're ready to build