feat: make VST3 an opt-in cargo feature

Cargo.toml declared Apache-2.0 while the default build linked vst3-sys,
whose bindings are GPLv3 — so the artifact a fresh clone produced could
not legally be distributed under the licence the repo claimed. A template
should not hand that trap to every project cloned from it.

NIH-plug already anticipates this: its `vst3` feature exists, in upstream's
own words, "mostly for GPL-compliance reasons". Taking `default-features =
false` and re-exporting `vst3` as a local opt-in makes the default build
CLAP-only and genuinely Apache-2.0 clean, while `--features vst3` remains
one flag away for anyone who accepts GPLv3.

Gating the feature rather than relicensing keeps the decision with whoever
uses the template. Reversing it is a one-line default plus removing two
cfg attributes, where relicensing to GPLv3 now would commit every
downstream plugin to that choice.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WHt4DykxXaQnyaJfyS8KCn

Cargo.toml

@@ -10,6 +10,14 @@ license = "Apache-2.0"
 [workspace]
 members = ["xtask"]
 
+[features]
+# CLAP only by default. NIH-plug's VST3 bindings (vst3-sys) are GPLv3, so linking
+# them makes the resulting binary GPLv3 regardless of what this package declares.
+# Opt in explicitly — and relicense this crate — if you intend to ship a VST3:
+#   cargo xtask bundle nih_plug_template --release --features vst3
+default = []
+vst3 = ["nih_plug/vst3"]
+
 [lib]
 # `cdylib` is the plugin binary; `lib` (rlib) lets `cargo test` link the unit tests.
 crate-type = ["cdylib", "lib"]
@@ -17,7 +25,8 @@ crate-type = ["cdylib", "lib"]
 [dependencies]
 # Pinned to the same commit as musiikki/codename-206.
 # Update the `rev` when you want to update NIH-plug.
-nih_plug = { git = "https://github.com/robbert-vdh/nih-plug.git", rev = "f36931f7af4646065488a9845d8f8c2f95252c23", features = ["assert_process_allocs"] }
+# `default-features = false` drops nih_plug's default `vst3` feature; see [features] above.
+nih_plug = { git = "https://github.com/robbert-vdh/nih-plug.git", rev = "f36931f7af4646065488a9845d8f8c2f95252c23", default-features = false, features = ["assert_process_allocs"] }
 nih_plug_egui = { git = "https://github.com/robbert-vdh/nih-plug.git", rev = "f36931f7af4646065488a9845d8f8c2f95252c23" }
 
 [profile.release]