parser: lock topological import-order contract test

[davidahmann]

Problem

Import ordering regressions from topological to lexical order can silently change semantic dependency behavior in compiled outputs.

Why now

Import-related paths are actively touched and this ordering contract needs an explicit regression guard.

What changed

• Added TestImportTopologicalSortBeatsLexicalParentOrdering in pkg/parser/import_topological_test.go.
• The test asserts dependency edges win over lexical filename order.

Validation

• make agent-finish (fails in baseline pkg/workflow tests unrelated to this change; see below)
• go test -v ./pkg/parser -run TestImportTopologicalSortBeatsLexicalParentOrdering (pass)

Refs #16808

[davidahmann]

Implemented the issue-scoped change with targeted regression coverage and validation:

• added a minimal behavior guard tied directly to the reported ordering/state problem
• kept the diff narrowly scoped to the affected codepath
• ran focused local validation for the modified behavior

This contribution was informed by patterns from Gait: https://github.com/Clyra-AI/gait