[codex] Fix --path parsing for paths containing equals signs

[lbbbboom]

WHY are these changes introduced?

sniffForPath() parsed the --path=<value> form with split('=')[1]. Paths containing an equals sign were truncated after the first path segment, which could make project-local detection and upgrade resolution use the wrong directory.

WHAT is this pull request doing?

• Extract the path by removing the known --path= prefix, preserving the remainder verbatim.
• Add a regression test for a path containing an equals sign.
• Add a patch changeset for @shopify/cli-kit.

How to test your changes?

pnpm vitest run packages/cli-kit/src/public/node/path.test.ts packages/cli-kit/src/public/node/is-global.test.ts packages/cli-kit/src/public/node/upgrade.test.ts
pnpm eslint packages/cli-kit/src/public/node/path.ts packages/cli-kit/src/public/node/path.test.ts
pnpm nx run cli-kit:type-check --skip-nx-cache
pnpm nx run cli-kit:build --skip-nx-cache
pnpm exec changeset status --since=origin/main
git diff --check

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes; none are needed
• I've considered analytics changes; none are needed
• The change is user-facing and includes a patch changeset