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 matters more than the allow list here: the ONNX
model weights this worker will load are licensed independently of the
`ort` crate, and `cargo deny` cannot see them at all. Ultralytics YOLO
and Obico's print-failure model are both AGPL-3.0 and cannot ship in a
commercial product - see continuum-common's docs/LICENSES.md, and pick a
permissive architecture before collecting training data rather than
retraining because of a licence.

deny.toml

@@ -0,0 +1,41 @@
+# Licence policy for a closed-source commercial product.
+# See docs/LICENSES.md in continuum-common for the rationale and the
+# non-cargo dependencies (external binaries, ML models) this file cannot see.
+#
+# Run: cargo deny check licenses
+
+[licenses]
+# Permissive only. Anything copyleft reaching a shipped binary would make
+# the product undistributable without releasing our source.
+allow = [
+    "MIT",
+    "Apache-2.0",
+    "Apache-2.0 WITH LLVM-exception",
+    "BSD-2-Clause",
+    "BSD-3-Clause",
+    "ISC",
+    "Zlib",
+    "Unicode-3.0",
+    "Unlicense",
+    "MPL-2.0",
+    "CC0-1.0",
+    "BlueOak-1.0.0",
+]
+confidence-threshold = 0.9
+
+# Our own crates declare `LicenseRef-Proprietary`, which is deliberately not
+# an SPDX identifier and must never appear in the allow list above - a
+# third-party crate claiming it would be a real finding. They are recognised
+# as first-party by `publish = false` in their manifests.
+private = { ignore = true }
+
+[bans]
+deny = []
+
+[advisories]
+yanked = "deny"
+
+# NOT VISIBLE TO THIS FILE: the ONNX model weights loaded at runtime carry
+# their own licence, independent of the `ort` crate (MIT). Ultralytics YOLO
+# and Obico's print-failure models are AGPL-3.0 and cannot ship in a
+# commercial product. See docs/LICENSES.md.