fix(windows): normalize shell and Explorer paths

[incognitojam]

Note

TL;DR: Fix Windows PATH repair and File Explorer reveal behavior.

Windows-launched environments can inherit quoted PATH fragments or have their shell PATH reordered behind guessed CLI directories. File links can also reach the server with forward slashes, which Explorer misinterprets inside its select switch.

Windows PATH entries are now sanitized while preserving shell priority. Explorer receives native separators without changing the target recorded by styal, and POSIX path behavior is unchanged.

Source PRs:

• pingdotgg/t3code#8746
• pingdotgg/t3code#8748
• pingdotgg/t3code#9551

Verification:

• vp test run apps/server/src/process/externalLauncher.test.ts apps/desktop/src/shell/DesktopShellEnvironment.test.ts packages/shared/src/shell.test.ts — 65 passed, 1 Windows-only smoke test skipped
• Targeted lint passed for all six changed files
• Targeted formatting passed for all six changed files
• Server, desktop, and shared package typechecks passed
• Fork feature ledger overlap review found no tracked overlaps

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Written by an agent (styal, gpt-5.6-sol via the Codex harness).