fix(plane): ax field names verbatim; pins and bindings as stripped annotations

Requirement 1.1 (Task/Workspace/Model use only fields ax documents) and
Requirement 1.4 (no ax field repurposed) were violated: manifests accepted
metadata.namespace and a Workspace git `commit`, and the reconciler dumped
every git field into what `ax apply` receives.

Facts from ax's source (pkg/apis/v1alpha1/ax.proto, internal/workspace/setup.go):
- ObjectMeta is `name` and `atespace` (plus server-set creation_timestamp);
  no `namespace`, no `annotations`.
- GitRepo is `name`, `repo`, `branch`, `dir`, `depth`; no `commit`.
- The API server decodes with protojson.UnmarshalOptions{}: an unknown field
  is an error at `ax apply` (confirmed on the live cluster: a rendered
  Workspace+Model applied cleanly; the same Workspace with `commit` was
  refused with `unknown field "commit"`).
- ValidateModel checks only metadata; any spec.provider string is accepted.

Changes:
- manifests: metadata takes `name`, `atespace`, `annotations` (our extension,
  never sent to ax); git entries take exactly ax's five fields (depth int);
  `commit` in spec.git is rejected with a pointer to the new Workspace
  annotation `openultrasast.io/git-commits: "<git name>=<40-hex>,..."`,
  validated for unknown git names and non-hex shas.
- reconciler: rendered docs carry only ax fields; each bound Workspace's pins
  reach the Task as env OUSAST_GIT_PINS = {"<workspace>/<git name>": "<sha>"}.
  A test walks every rendered doc against ax's field lists.
- runner: pins come from OUSAST_GIT_PINS; git is fetched as setup.go does
  (init/remote/fetch with --depth when depth > 0/checkout FETCH_HEAD, default
  branch main, cloneDestination's dir and placeholder-name rules), then the
  pin is checked out. A pinned entry without a branch fetches the commit.
- workspaces: emits the annotation, `dir: repo` and `depth: 1` instead of
  `commit`, so generated case workspaces keep <path>/repo at depth 1.
- design.md: ax field names verbatim; pins and model binding as stripped
  openultrasast.io/* annotations carried to the task by env.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

tests/fixtures/plane/smoke-task.yaml

@@ -0,0 +1,29 @@
+# Minimal Task for the bring-up smoke test: default runner image, a files-only workspace, no MCP or skills.
+apiVersion: ax.io/v1alpha1
+kind: Task
+metadata:
+  name: ousast-smoke
+  atespace: default
+spec:
+  image: "gcr.io/ax-substrate/ate-images/ax-task-runner@sha256:3a0dea6ad8b55278685db58aca6e37dc4ba04056831d45bef3aaeafdca43cac6"
+  command: ["sh", "-c", "cat /workspace/hello.txt && echo smoke-ok"]
+  resources:
+    requests:
+      cpu: "100m"
+      memory: "256Mi"
+    limits:
+      cpu: "1"
+      memory: "1Gi"
+  workspaces:
+    - name: ousast-smoke-ws
+      path: "/workspace"
+---
+apiVersion: ax.io/v1alpha1
+kind: Workspace
+metadata:
+  name: ousast-smoke-ws
+  atespace: default
+spec:
+  files:
+    - path: "hello.txt"
+      content: "hello from openultrasast\n"