refactor: drop internal bridge/ffi layers; exporter family lands

Single-lib cleanup: the per-crate src/bridge/ and src/ffi.rs layers are
gone (oakundo/oakcommon/oaknode/oaktimeline/oakcodec/oakaudio/
oakrender/oaktask/oakplugin/oakstorage); cross-crate calls are plain
Rust, CHandle marshalling shrinks to the oakengine boundary, and tests
call the Rust APIs directly (pure C-ABI wrapper tests removed where
the domain layer already covers the behavior).

exporter.h family implemented: oakengine_export_render (CLI contract),
oakengine_export_render_with_params (was a stub), last_error and
progress callback; synchronous path reuses task_create_export +
start_sync. Fixes on the way: oaktask video ticket self-deadlock,
audio params dropped on the export path, codec encoder AAC slicing and
H.264 time base. Real-mp4 tests cover both entry points, progress and
the illegal-argument matrix.

Also: oakstorage session maps null project handles to None (version-
info path), configstore test double literal 3.14 -> 3.15 (clippy PI
lint), oakaudio output callback scratch buffer + env-aware P1 test,
cli media round-trip test uses a generated 16-frame clip (no more
minute-long debug runs).

crates/oaktask/src/handle.rs

@@ -40,10 +40,6 @@ pub struct RefBox<T: ?Sized> {
 /// source-compatible. `Send + Sync` come from the shared type.
 pub use oakcore_rs::handle::CHandle;
 
-unsafe extern "C" fn noop_addref(_ctx: *mut std::ffi::c_void) {}
-
-unsafe extern "C" fn noop_release(_ctx: *mut std::ffi::c_void) {}
-
 unsafe extern "C" fn owned_addref<T: 'static>(ctx: *mut std::ffi::c_void) {
 	if !ctx.is_null() {
 		// CPP-PARITY: src/task/c_api/taskhandle.h (task_addref)