feat: built-in effect params, clip click-select, effect drag-and-drop, project load with plugins

- serializer resolves node types through the factory's dynamic
  (runtime-registered OpenFX) entries, so a project carrying plugin
  nodes loads again (was: "unknown node type"); covered by a new
  CI-gated round-trip test driving the real fixture plugin
- built-in effect nodes expose their inputs as inspector parameters
  like the C++ parameter editor: localized input names from the
  behavior, combo option tables via the new
  NodeBehavior::input_combo_strings (16 nodes, string-for-string from
  the C++ set_combo_box_strings), connection/data inputs excluded
- effect library: live drag-and-drop — onto the inspector's effect
  stack (lands at the indicator position) and onto the node editor
  canvas (creates the node at the drop point); double-click still
  appends to the selected clip
- inspector parameter controls are no longer recreated per render
  (gpui stack view caches them per effect), so sliders drag and
  checkboxes click; the view observes the engine and silently re-syncs
  values (undo/redo land on the widgets)
- timeline: left-press selects clips (plain/keep-multi/Ctrl-Cmd
  toggle); clip moves clamp the shared delta so no clip of a linked
  group lands before frame 0 instead of failing with "invalid move
  target"
- oakplugin: createInstance-rejected instances skip the destroyInstance
  notification (the plugin never owned them); vendor-suite fetchSuite
  misses moved behind OAK_OFX_TRACE; the worker logs the discovered/
  registered plugin counts
- CI: the OFX probe step also runs the serialization round-trip test
- gpui submodule: params view caching, clip click-select, library
  drag payload, graph_position_at

.github/workflows/ci.yml

@@ -196,3 +196,7 @@ jobs:
           OFX_PLUGIN_PATH="$PWD/.cache/ofx-fixture" \
             cargo run --locked -p oakplugin --example scan_probe > probe.log 2>&1
           grep -q 'type_id=rs.oak.CiTestPlugin' probe.log
+          # A project carrying a plugin node must survive save/load (the
+          # serializer resolves plugin types via the dynamic factory).
+          OAK_OFX_FIXTURE_DIR="$PWD/.cache/ofx-fixture" \
+            cargo test --locked -p oakplugin --test ofx_roundtrip