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/Cargo.toml

@@ -15,14 +15,7 @@ oakundo = { path = "../oakundo" }
 oakcodec = { path = "../oakcodec" }
 thiserror = "2"
 
-[features]
-# In-crate stubs for the oakundo C ABI (and other module bridges) so
-# cargo test can exercise the undoable exports end-to-end without the
-# module libraries; real builds (feature off) dlsym the actual modules.
-test-stubs = []
-
 [dev-dependencies]
-# oakcodec's oakcore_*/oakrender_* host-mocks (test-stubs feature): the
-# node test binaries link the real oakcodec (footage probe), whose ffmpeg
-# unit references those cross-crate symbols that no Rust crate provides.
-oakcodec = { path = "../oakcodec", features = ["test-stubs"] }
+# oakcodec is also a plain dependency above; the dev-dependency re-entry
+# used to enable oakcodec's `test-stubs` host-mocks, which no longer exist
+# (single-lib unification removed the oakcore_*/oakrender_* C ABI calls).