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/oaknode/src/nodes/polygon.rs

@@ -136,7 +136,7 @@ impl NodeBehavior for PolygonGenerator {
 	/// scaling and center translation; without a backend the frame is
 	/// left empty (warned once).
 	///
-	/// The Rust `frame` is an opaque [`crate::bridge::render::TextureHandle`]
+	/// The Rust `frame` is an opaque [`crate::handle::CHandle`]
 	/// whose bytes cannot be touched, and this crate has no path-fill
 	/// backend — so neither the clear nor the fill is representable here
 	/// (`// CPP-PARITY: polygon.cpp` `generate_frame`). The path building
@@ -145,7 +145,7 @@ impl NodeBehavior for PolygonGenerator {
 	fn generate_frame(
 		&self,
 		core: &NodeCore,
-		frame: &mut crate::bridge::render::TextureHandle,
+		frame: &mut crate::handle::CHandle,
 		time: oakcore_rs::Rational,
 	) {
 		let _ = (core, frame, time);