refactor: workspace layout — crates/, app at root, legacy C++ removed

Single mechanical restructure commit:
- root Cargo.toml = oakapp bin + workspace; one cargo build produces
  oakapp, oak-cli, oak-worker, liboakengine.dylib
- app/rust/src -> src/ (app at repo root, no rust/ nesting)
- src/<mod>/rust -> crates/oak<mod>; src/oakcore-rs -> crates/oakcore;
  src/bindings/oakotio -> crates/oakotio; src/engine/rust ->
  crates/oakengine (keeps cdylib+staticlib+rlib)
- public C headers include/<mod>/ -> crates/oakengine/include/<mod>/
- OFX SDK headers vendored into crates/oakplugin/ofx/ (HostSupport gone)
- legacy deleted: old src/ C++ modules, engine/, core/, ffmpeg_bridge/,
  app/ (Qt), cli/worker C++, root CMakeLists, third_party/KDDockWidgets
  submodule, otio-install, all build-* output (~40GB)
- oakstorage kept but excluded from the workspace (skeleton w/ todos);
  gpui excluded (own workspace)
- verified: cargo build green, cargo test --workspace 1845/0
  (with the documented OCIO_RS_* env override for the homebrew OCIO)

crates/oaknode/src/input.rs

@@ -0,0 +1,96 @@
+// Oak Video Editor - Non-Linear Video Editor
+// Copyright (C) 2026 Oak Team
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Input descriptors: the C++ `Node::Input` record, flags, array
+//! inputs, and value hints.
+
+use crate::value::{NodeValue, ValueType};
+
+/// Input flag bits (values match the C++ `InputFlag` enum — they
+/// cross the C ABI and project XML as ints).
+pub mod flags {
+	/// Not connectable to other nodes.
+	pub const NOT_CONNECTABLE: u32 = 1 << 0;
+	/// Not keyframable.
+	pub const NOT_KEYFRAMABLE: u32 = 1 << 1;
+	/// Array input (elements addressable).
+	pub const ARRAY: u32 = 1 << 2;
+	/// Hidden from the parameter UI.
+	pub const HIDDEN: u32 = 1 << 3;
+	/// Does not trigger invalidation on change.
+	pub const IGNORE_INVALIDATIONS: u32 = 1 << 4;
+}
+
+/// One input (scalar) or one array element slot's descriptor.
+#[derive(Clone)]
+pub struct Input {
+	/// Input id (e.g. "tex_in").
+	pub id: String,
+	/// Accepted value type.
+	pub value_type: ValueType,
+	/// Default value (C++ default parameter).
+	pub default: NodeValue,
+	/// Flag bits (`flags::*`).
+	pub flags: u32,
+	/// Display name (C++ `set_input_name`).
+	pub display_name: String,
+	/// Arbitrary properties (C++ `set_input_property` map).
+	pub properties: Vec<(String, NodeValue)>,
+	/// Array size for ARRAY inputs (0 otherwise).
+	pub array_size: usize,
+}
+
+impl Input {
+	/// New input with the given id/type/default and normal flags.
+	pub fn new(id: &str, value_type: ValueType, default: NodeValue) -> Input {
+		Input {
+			id: id.to_string(),
+			value_type,
+			default,
+			flags: 0,
+			display_name: id.to_string(),
+			properties: Vec::new(),
+			array_size: 0,
+		}
+	}
+
+	/// Convenience accessor for the flag bits.
+	pub fn flags(&self) -> u32 {
+		self.flags
+	}
+
+	/// True when this is an array input (elements addressable).
+	pub fn is_array(&self) -> bool {
+		self.flags & flags::ARRAY != 0
+	}
+
+	/// True when the input accepts connections.
+	pub fn is_connectable(&self) -> bool {
+		self.flags & flags::NOT_CONNECTABLE == 0
+	}
+}
+
+/// Value hint (C++ `Node::ValueHint`): accepted type set per input,
+/// used to convert values on connect.
+#[derive(Clone, Debug, Default)]
+pub struct ValueHint {
+	/// Accepted types in preference order.
+	pub types: Vec<ValueType>,
+	/// Optional index hint.
+	pub index: i32,
+	/// Optional tag (e.g. track reference).
+	pub tag: String,
+}