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.

tooling/ffmpeg/build-ffmpeg.sh

@@ -15,7 +15,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-# Builds a project-owned FFmpeg for the oakcodec/oakaudio `ffmpeg-next`
+# Builds a project-owned FFmpeg for the oak-codec/oak-audio `ffmpeg-next`
 # dependency and installs it into .cache/ffmpeg. Point cargo at it with:
 #
 #   export FFMPEG_DIR="$(pwd)/.cache/ffmpeg"

tooling/install-deps.sh

@@ -17,7 +17,7 @@
 
 # Installs the system dependencies of the Oak Rust workspace:
 # the free-license external codec/filter libraries FFmpeg is configured
-# with (see crates/oakcodec/Cargo.toml), plus the build tools. FFmpeg
+# with (see crates/oak-codec/Cargo.toml), plus the build tools. FFmpeg
 # itself is built from source by tooling/ffmpeg/build-ffmpeg.sh (which
 # installs into .cache/ffmpeg) and is NOT installed here.
 #