feat: add OBS recording engine and validation probe

clipbin-obs starts the pinned libobs on a dedicated thread, opens exactly the
bundled plugin allowlist, and records official capture sources through one
hardware encoder into keyframe-aligned Matroska segments. Status reaches
Recording only once the source has a picture and the segment grows on disk.

clipbin-probe lists and verifies hardware encoders and records from a real
capture source, printing status, health and segment events for validation.

crates/clipbin-obs/src/lib.rs

@@ -0,0 +1,18 @@
+//! Clipbin's recording engine on top of the pinned libobs runtime.
+//!
+//! Capture uses only official OBS sources: Game Capture and Window Capture on
+//! Windows, Xcomposite on X11, and PipeWire through the desktop portal on
+//! Wayland. See SPEC.md.
+
+pub mod capture;
+pub mod encoders;
+mod ffi;
+mod recorder;
+pub mod runtime;
+mod thread;
+
+pub use recorder::{
+    Engine, EngineError, Health, RecorderEvent, Recording, RecordingConfig, SEGMENT_EXTENSION,
+    StatusTracker, StopReason, VideoFormat,
+};
+pub use runtime::{RuntimeError, RuntimeLayout};