Add upstream submodule path helpers, detection checks, and tests; update npm scripts

[jooh]

Motivation

• Treat upstream/ as the canonical source for vendored upstream CLI code and detect duplicate upstream-owned files outside the submodule.
• Provide shared path helpers and automated scans to rewrite and validate references that still point at root-level upstream assets.
• Add a fast-failing CI guard so pipeline jobs clearly fail when the upstream/ submodule is missing or uninitialized.

Description

• Added src/spec-node/migration/upstreamPaths.ts which centralizes the upstream submodule root and exposes shared path builders/constants used by npm/test scripts.
• Enhanced the readiness evaluator in src/spec-node/migration/upstreamSubmoduleCutoverReadiness.ts with file-scanning helpers and exported collectRootLevelUpstreamPathReferences(...) to detect root-level references that should be rewritten to upstream/....
• Added build/check-upstream-submodule.js to verify that the upstream/ submodule exists, contains required assets, and is initialized, and exposed it as the npm script check-upstream-submodule.
• Updated package.json test scripts to execute upstream test suites under upstream/src/test/... and added the check-upstream-submodule script.
• Added unit tests src/test/upstreamPaths.test.ts and expanded src/test/upstreamSubmoduleCutoverReadiness.test.ts to cover duplicate detection and root-level reference scanning behavior.
• Removed the legacy azure-pipelines.yml file as part of CI/workflow cleanup.

Testing

• Ran the unit test suite via npm test which exercises the new path helpers and the upstream cutover readiness checks, and all tests passed.
• Executed the new submodule guard via node build/check-upstream-submodule.js in a healthy checkout and confirmed it exits successfully when upstream/ is present and initialized.
• Verified the added tests under src/test cover duplicate path detection and root-level reference scanning and reported no failures.

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Codex Task

[jooh]

@codex review

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Handle glob tokens when extracting path references

The new path-candidate regex does not include */**, so common script arguments like src/test/**/*.test.ts are truncated to src/test before validation. In practice this can hide real root-level upstream references: if src/test exists locally (as it does here), includeExistingLocalPaths suppresses the match and the scanner reports no issue even though the original command still points at a non-upstream/ path. This weakens the migration/readiness check for mocha-style globbed test commands.

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[jooh]

@fix suggestions