render: apply clip effect stacks in the montage path

Adding an effect to a clip did nothing: the sequence render is
flattened into a montage (decode + composite), and MontageClip carried
no effect data at all.

- MontageClip gains an ordered effect stack (type id / enabled /
  effect input / parameter values); protocol v2 carries it as an
  additive wire field (older peers default to an empty stack).
- renderops::video_montage fills the stack from the effect chain
  (the footage source node — the chain end without an effect input —
  is dropped; the montage decodes the footage itself). Export
  (oak-task) and the multicam single-track montage fill it too.
- The worker applies the stack between decode and composite: built-in
  Opacity gets a CPU evaluator (C++ opacity.frag parity — whole vec4,
  alpha included, unity pass-through); everything else dispatches as an
  OFX plugin job through a new instance-factory slot (oak-plugin
  lazily creates + caches one instance per identifier per render
  process) with the montage's parameters injected. Disabled effects
  bypass (the C++ traverser pushes the effect input through). Unknown
  types warn once per type id and pass through — no silent no-ops.

Not covered (explicitly): Transform/Crop and the other ~30 built-in
effects have no CPU evaluator in oak-render (they pass through with a
warning), keyframed parameter animation, audio effect chains, and the
CLI's simplified montage.

Acceptance: a real 50% Opacity on real media quarters the rendered
pixels both in-process (renderops test) and through a real worker
process over IPC + shared memory (procpool_integration test);
disabling restores the plain render byte-for-byte.

crates/oak-worker/src/worker.rs

@@ -975,6 +975,7 @@ impl WorkerSession {
 				out_time: Rational::new(c.out_num, c.out_den),
 				media_in: Rational::new(c.media_in_num, c.media_in_den),
 				gain: c.gain,
+				effects: c.effects.iter().map(crate::ipc::montage_effect_from).collect(),
 			})
 			.collect();
 		Ok(AudioTicketParams {
@@ -1069,6 +1070,7 @@ impl WorkerSession {
 				out_time: Rational::new(c.out_num, c.out_den),
 				media_in: Rational::new(c.media_in_num, c.media_in_den),
 				gain: c.gain,
+				effects: c.effects.iter().map(crate::ipc::montage_effect_from).collect(),
 			})
 			.collect();
 		VideoTicketParams {