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/oakrender/src/commonutil.rs

@@ -0,0 +1,87 @@
+// 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/>.
+
+//! oakcommon helpers (config, file functions) — direct Rust calls into
+//! the oakcommon crate (single-lib unification; the former
+//! `bridge/common.rs`). The configuration-location and disk-cache
+//! helpers delegate to oakcommon's own implementation.
+
+use std::sync::Mutex;
+
+/// Read a config string via the domain store
+/// (`ConfigStore::get(group, key)`); `None` when missing or empty.
+pub fn config_get_string(group: Option<&str>, key: &str) -> Option<String> {
+	oakcommon::configstore::ConfigStore::instance()
+		.get(group, key)
+		.ok()
+		.filter(|s| !s.is_empty())
+}
+
+/// `oakcommon_config_get_int(group, key, default)`.
+pub fn config_get_int(group: Option<&str>, key: &str, default: i32) -> i32 {
+	oakcommon::configstore::ConfigStore::instance().get_int(group, key, default)
+}
+
+/// The configuration directory — oakcommon's implementation
+/// (`FileFunctions::get_configuration_location`, honoring `OAK_CONFIG_DIR`
+/// and the platform fallbacks).
+pub fn configuration_location() -> String {
+	oakcommon::filefunctions::FileFunctions::new()
+		.get_configuration_location()
+		.unwrap_or_default()
+}
+
+/// Serializes tests that mutate `OAK_CONFIG_DIR` / `OAK_RENDER_BACKEND`
+/// (env is process-global; the manager tests share this lock too).
+pub static ENV_TEST_LOCK: Mutex<()> = Mutex::new(());
+
+/// The default disk cache directory (C++ `DiskManager::
+/// get_default_disk_cache_path`): `<configuration_location>/mediacache`.
+pub fn default_disk_cache_path() -> String {
+	oakcommon::filefunctions::default_disk_cache_path()
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn config_missing_key_falls_back() {
+		// The real config store is empty under cargo test: defaults apply.
+		assert_eq!(config_get_int(None, "GraphicsBackend", 7), 7);
+		assert_eq!(config_get_string(None, "missing"), None);
+	}
+
+	#[test]
+	fn configuration_location_uses_env_override() {
+		let _guard = ENV_TEST_LOCK.lock().unwrap_or_else(|e| e.into_inner());
+		let dir = std::env::temp_dir().join("oakrender-config-test");
+		std::env::set_var("OAK_CONFIG_DIR", &dir);
+		let loc = configuration_location();
+		assert_eq!(loc, dir.to_string_lossy());
+		std::env::remove_var("OAK_CONFIG_DIR");
+	}
+
+	#[test]
+	fn default_disk_cache_path_is_under_config() {
+		let _guard = ENV_TEST_LOCK.lock().unwrap_or_else(|e| e.into_inner());
+		let dir = std::env::temp_dir().join("oakrender-cache-test");
+		std::env::set_var("OAK_CONFIG_DIR", &dir);
+		let p = default_disk_cache_path();
+		assert!(p.ends_with("/mediacache") || p.ends_with("\\mediacache"));
+		std::env::remove_var("OAK_CONFIG_DIR");
+	}
+}