feat(resource): add deferred virtual resource types

Add 3 deferred virtual resource types (remote, submodule, symlink) with
equivalence metadata for physical-to-virtual resource linking.

Depends on: #662 (child_types reference types introduced by #662)

- Type definitions extracted to _resource_registry_virtual_deferred.py
  for consistency with _resource_registry_virtual.py (#329)
- YAML configs with equivalence criteria per spec, spec reference comments
- Bootstrap registration via BUILTIN_TYPES spread, hidden from
  resource add scaffolding (user_addable: false)
- Equivalence structural validation in ResourceTypeSpec model validator:
  criteria must be a non-empty list of non-empty strings; virtual types
  must have sandbox_strategy=none, user_addable=false, handler=None,
  all capabilities false
- Behave tests (52 scenarios), Robot tests (7), ASV benchmarks
- DB roundtrip tests verifying virtual types survive bootstrap persistence
- Negative tests: missing equivalence/name/kind, manual add rejection
  for all 3 virtual types (register_resource guard), invalid criteria
  elements (non-string, empty string)

ISSUES CLOSED: #331

examples/resource-types/remote.yaml

@@ -0,0 +1,20 @@
+# Spec reference: docs/specification.md ~lines 23705-23719, 24619-24631
+schema_version: "1.0"
+name: remote
+description: "Cross-repo remote identity. Links git-remote resources across different repos that point to the same URL."
+resource_kind: virtual
+sandbox_strategy: none
+user_addable: false
+built_in: true
+cli_args: []
+parent_types: []
+child_types: ["git-remote"]
+capabilities:
+  read: false
+  write: false
+  sandbox: false
+  checkpoint: false
+equivalence:
+  criteria: ["url"]
+  description: "Two git-remote resources share a remote parent when they point to the same normalized URL."
+handler: null

examples/resource-types/submodule.yaml

@@ -0,0 +1,20 @@
+# Spec reference: docs/specification.md ~lines 23705-23719, 24619-24631
+schema_version: "1.0"
+name: submodule
+description: "Cross-repo submodule identity. Links git-submodule resources across different repos with the same submodule URL and path."
+resource_kind: virtual
+sandbox_strategy: none
+user_addable: false
+built_in: true
+cli_args: []
+parent_types: []
+child_types: ["git-submodule"]
+capabilities:
+  read: false
+  write: false
+  sandbox: false
+  checkpoint: false
+equivalence:
+  criteria: ["url", "path"]
+  description: "Two git-submodule resources share a submodule parent when they have the same submodule URL and path."
+handler: null

examples/resource-types/symlink.yaml

@@ -0,0 +1,20 @@
+# Spec reference: docs/specification.md ~lines 23705-23719, 24619-24631
+schema_version: "1.0"
+name: symlink
+description: "Cross-layer symlink identity. Links fs-symlink and git-tree-entry (mode 120000) resources with the same name and target."
+resource_kind: virtual
+sandbox_strategy: none
+user_addable: false
+built_in: true
+cli_args: []
+parent_types: []
+child_types: ["fs-symlink", "git-tree-entry"]
+capabilities:
+  read: false
+  write: false
+  sandbox: false
+  checkpoint: false
+equivalence:
+  criteria: ["name", "target_path"]
+  description: "Two physical symlink resources share a symlink parent when they have the same name and target path."
+handler: null