fix(import): harden WinSCP password and site import reliability

[Orinks]

Replacement for #77 with clean commit history to satisfy GitGuardian.

Includes:

• WinSCP decrypt reliability fixes (upstream-aligned)
• INI encoding/URL-decoding hardening
• WinSCP-specific import UX messaging
• sanitized fixture + runtime-generated encrypted test values

Supersedes #77.

[gitguardian]

⚠️ GitGuardian has uncovered 2 secrets following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

🔎 Detected hardcoded secrets in your pull request

GitGuardian id	GitGuardian status	Secret	Commit	Filename
27836301	Triggered	Generic Password	f31d82b	tests/fixtures/importers/winscp_real_export_sanitized.ini	View secret
27836302	Triggered	Generic Password	f31d82b	tests/fixtures/importers/winscp_real_export_sanitized.ini	View secret

🛠 Guidelines to remediate hardcoded secrets

1. Understand the implications of revoking this secret by investigating where it is used in your code.
2. Replace and store your secrets safely. Learn here the best practices.
3. Revoke and rotate these secrets.
4. If possible, rewrite git history. Rewriting git history is not a trivial act. You might completely break other contributing developers' workflow and you risk accidentally deleting legitimate data.

To avoid such incidents in the future consider

• following these best practices for managing and storing secrets including API keys and other credentials
• install secret detection on pre-commit to catch secret before it leaves your machine and ease remediation.

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^{🦉 GitGuardian detects secrets in your source code to help developers and security teams secure the modern development process. You are seeing this because you or someone else with access to this repository has authorized GitGuardian to scan your pull request.}

[Orinks]

Closing in favor of original PR #77 (branch force-updated with clean history).