feat(edit): expose connection authoring through ApplyEdits and the clients

[devin-ai-integration]

What and why

Closes #599 and #601. The edit layer already writes connection-like usages (edit.OpAddConnection, used by the LSP), but ApplyEdits had no operation for them, so the Python, Go and Java clients couldn't author an allocation or a flow. add_member(kind="allocate") was never the right path: an allocation or flow is a connection between two feature ends, not a named member.

This PR exposes the existing operation. The edit-layer writer is unchanged.

message EditOperation { oneof operation { ...; AddConnectionEdit add_connection = 6; } }
message AddConnectionEdit { string owner = 1; string kind = 2; string from_end = 3; string to_end = 4; string name = 5; string type = 6; }

• gRPC: add_connection maps to edit.AddConnection(owner, kind, from, to, name) with Type. It requires authoring plus a new connection_authoring capability. An older service advertises authoring but can't decode oneof arm 6, so the extra capability lets a client refuse locally instead of getting INVALID_ARGUMENT for an unset operation. The Go, Python and Java clients check both before sending.
• Python: Editor.add_connection(owner, kind, from_, to, name=None, type=None), plus add_allocation(owner, from_, to, ...) and add_flow(owner, from_, to, ...). The fields are from_end/to_end because from is a Python keyword.
• Go: opensysml.AddConnection{Owner, Kind, From, To, Name, Type}. Java: Edit.AddConnection.of(owner, kind, from, to).withName(..).withType(..).
• Stubs regenerated for Go, Python, Java, TypeScript and Rust with make proto.

Example: model.edit().add_allocation("Demo::System", "a", "b", name="alloc1").apply() inserts allocation alloc1 allocate a to b;, and add_flow("Demo::System", "tank.fuelOut", "engine.fuelIn") inserts flow from tank.fuelOut to engine.fuelIn;.

Specification basis

The written forms are the ones the edit layer already produces, and each is a production of the pinned SysML v2 grammar: AllocationUsage (allocation [decl] allocate a to b), FlowConnectionUsage (flow [decl] from a to b), ConnectionUsage/InterfaceUsage (connect a to b), BindingConnectorAsUsage (bind a = b), SuccessionAsUsage (first a then b), plus the KerML Connector/BindingConnector/ItemFlow/Succession forms. A type is accepted only for kinds whose declaration admits one, so succession with a type is refused as an illegal kind. Every edit is re-parsed and re-analysed, and an edit that introduces errors (for example an unresolved end) is refused. No spec-compliance rows move.

How it was verified

• go test ./internal/frontend/grpc/... ./internal/check/edit/... ./client/opensysml/... ./tests/grpc/... and go test -C tools ./cmd/conformance/.... New tests: allocation, flow and typed-connection round trips; refusals for an unknown kind, a type on a succession and an unresolved end; the authoring and connection_authoring gates (the service refuses add_connection without connection_authoring while add_member still works, and each client refuses before sending); a golden add_connection case.
• Python test_edit.py / test_wire_compat.py (100 passed), including a live allocation round trip against sysml-grpc.
• Java EditProtosTest and build. Java conformance: 260 passed, 0 failed, 10 skipped, including the new apply_edits/an_allocation_is_written_between_two_features scenario. Node and Rust runners skip ApplyEdits scenarios, as before.
• make lint, make docs-check, python3 scripts/changelog.py check, make proto-lint proto-breaking (additive only), git diff --check.

Checklist

• make test and make lint pass locally (make lint and the focused suites above; the full make test is left to CI)
• Tests added or updated for the change
• Documentation extended where it already covers the surface (see CONTRIBUTING.md)
• Changelog entry added as changes/unreleased/<slug>.<section>.md, not as an edit to CHANGELOG.md
• baselines regenerated and make docs-counts run if a gate count moved (no gate count moved)
• No internal work-item labels (waves, slices, F4, K5) in the body, docs, or changelog

[devin-ai-integration]

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