Fix Windows PATH handling for launcher installs

[t-kalinowski]

Summary

• Persist launcher directories in the Windows user-level Path even when they are already present only in the live process PATH, without clobbering that live PATH
• Use a short Windows path when available, with duplicate checks against both canonical and short forms
• Add a clearer guard and user hint for the 32767-character PATH limit
• Exclude .git from source builds so local worktree metadata does not show up in package checks
• Document the Windows PATH handling fix in NEWS.md for Fix Windows PATH handling for launcher installs #38

Testing

• testthat::test_local() passed
• R CMD build . passed
• R CMD check --no-manual Rapp_0.3.0.9000.tar.gz passed

[chatgpt-codex-connector]

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