workspace: kebab-case crates, app under crates/oak-app, shared versions

All crates take the oak-* kebab-case naming (oak-audio, oak-codec,
oak-common, oak-core, oak-ffmpeg-link, oak-node, oak-otio, oak-plugin,
oak-render, oak-storage, oak-task, oak-timeline, oak-undo), with the
lib identifiers rewritten (oakrender:: -> oak_render::, oakcore_rs:: ->
oak_core::, ...) across all 226 referencing files.

The GUI application moves from the workspace root into
crates/oak-app/: src/, build.rs (paths fixed for the new location) and
tests/ travel with it, the root Cargo.toml becomes workspace-only
([workspace] + workspace.package + profiles), and the app package
inherits the workspace version. The screenshots example becomes a
standalone crate examples/simple_player/ with its own Cargo.toml.

Every crate now inherits the single workspace version
(version.workspace = true), and the workflows' crate paths and the
build docs follow the renames.

Validated with a clean cargo check --workspace.

docs/build.md

@@ -33,7 +33,7 @@ macOS, Linux, and Windows. For the Chinese version see
   `FFMPEG_DIR` does not need exporting: the committed
   `.cargo/config.toml` sets it relative to the workspace root
   (`ffmpeg-sys-next` cannot read `.env` at build-script time — the
-  config entry is the only machine-agnostic way). The `oakffmpeg-link`
+  config entry is the only machine-agnostic way). The `oak-ffmpeg-link`
   build script panics without it; run `build-ffmpeg.sh` once before the
   first `cargo build`.
 
@@ -128,7 +128,7 @@ Unix-style link args the MSVC linker rejects).
 
 Without the `bundled` feature and without `OCIO_RS_ENABLE_REAL=1`,
 `ocio-sys` builds a stub and every colour test early-returns. The
-bundled feature is enabled unconditionally by `oakrender`, so a plain
+bundled feature is enabled unconditionally by `oak-render`, so a plain
 `cargo build` always gets the real thing on Linux/macOS.
 
 ## Packaging
@@ -149,7 +149,7 @@ libraries; see `docs/project-storage.md` for what lands where.
 
 ## Troubleshooting
 
-- **`oakffmpeg-link` panics about `FFMPEG_DIR`** — run
+- **`oak-ffmpeg-link` panics about `FFMPEG_DIR`** — run
   `tooling/ffmpeg/build-ffmpeg.sh` once; it installs into
   `.cache/ffmpeg`, which `.cargo/config.toml` points at.
 - **IDE builds fail (RustRover etc.)** — IDEs that cannot inject