feat(plane): manifest schemas and validation (task 1)

Add openultrasast.plane.manifests: frozen dataclasses and loaders for ax's
Task, Workspace and Model kinds (ax.io/v1alpha1, ax's fields only) and the
Run kind (openultrasast.io/v1alpha1: tasks, dependsOn, inputs, outputs,
budget, serialize). Every violation raises ManifestError naming the kind,
metadata.name and field path: unknown fields at any depth, wrong apiVersion
or kind, a provider outside google/anthropic unless deepseek is declared via
the openultrasast.io/provider-extension annotation, a Run with a dependency
cycle, an input naming no task, and a Run task naming no loaded Task.
load_manifests reads multi-document YAML files and indexes by kind and name.

PyYAML becomes the one declared core dependency; the two zero-dependency
guards now pin exactly that, and the module audit registers the plane
package under the ai-service-plane spec.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

src/openultrasast/model/audit.py

@@ -54,6 +54,8 @@ SPEC_OWNED = {
     "cpg": "model-grounded-detection Req 4: the CPG seam package",
     "cpg.backend": "model-grounded-detection Req 4.1/4.5: the single Joern subprocess boundary",
     "cpg.capability": "model-grounded-detection Req 4.2/4.3: the engine probe that degrades to suspicion",
+    "plane": "ai-service-plane Req 1: the model-level service plane package; reconciler and runner land in tasks 3-4",
+    "plane.manifests": "ai-service-plane Req 1.1-1.4: ax-shaped Task/Workspace/Model and the Run kind, validated before anything runs",
 }
 
 STANDALONE = {