Fix Windows install and review edge cases

[ShiroKSH]

Summary

• Normalize Amp workspace and binary candidate paths across platforms.
• Keep the PowerShell installer parseable under Windows PowerShell and make installer tests line-ending safe.
• Abort active Ask AI server turns when sessions or threads reset.
• Match Bun behavior for empty Pi archive entries and Pi config label persistence.
• Drop debug logging on expected browser fallback paths.

Validation

• bun test apps/amp-plugin/plannotator.test.ts scripts/install.test.ts
• bun test apps/pi-extension/server.test.ts -t 'pi plan archive server'
• PowerShell parser check for scripts/install.ps1
• bun run typecheck with Git Bash on PATH

Notes

Full bun test still has unrelated Windows failures in symlink, semantic-diff, temp-lock, and path-expectation suites.