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/oakengine/src/test_support/mod.rs

@@ -0,0 +1,52 @@
+// Oak Video Editor - Non-Linear Video Editor
+// Copyright (C) 2026 Oak Team
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Unit-test aggregation for the oakengine facade (single-lib unification).
+//!
+//! The facade's crate-type is cdylib-only (no rlib), so the former
+//! `tests/*.rs` integration tests cannot link `oakengine` as a crate.
+//! They moved here (`src/test_support/`, pulled in by `src/lib.rs` under
+//! `#[cfg(test)]`) and run as unit tests against `crate::*` instead of
+//! `oakengine::*`. The old `#[path = "common/mod.rs"] mod common;` include
+//! is replaced by the single [`common`] declaration below — the
+//! `oakcore_*` mock symbols it defines may exist only once per binary.
+//!
+//! The node/timeline/render-graph families (and the graph-op tests that
+//! built fixtures through the deleted handle-based module C ABIs) are
+//! part of the pending domain-model redesign; their test files were
+//! deleted with this migration (see the migration report).
+
+#![allow(dead_code)]
+
+#[path = "common/mod.rs"]
+pub mod common;
+
+mod audio;
+mod codec;
+mod common_smoke;
+mod it_audio;
+mod it_codec;
+mod it_common;
+mod it_export;
+mod it_plugin;
+mod it_task;
+mod it_undo;
+mod linkage;
+mod node;
+mod plugin;
+mod render;
+mod task;
+mod undo;