Improve per-session SFTP and Hosts management

[bifrost0x]

Summary

• scope embedded SFTP capability and visibility to each active SSH session
• keep incompatible sessions closed while preserving a manual fallback for inconclusive probes
• keep Hosts controls fixed, focus search on open, and add Collapse all

Behavior

• switching from Linux to a Cisco-style session closes embedded SFTP without retargeting the panel
• switching back restores the Linux session's own open or closed preference
• all eligible desktop sessions are capability-probed regardless of session count
• disconnects and layout changes cancel pending probe retries without misclassifying the session
• known-unavailable sessions keep the embedded SFTP control disabled
• search, Collapse all, and Create saved connection remain visible while only the host list scrolls

Tests

• npm run test:js (228 passed)
• npm run lint:js
• npm run vendor:check
• python -m pytest tests -q (1605 passed, 33 skipped)
• affected Python UI contracts (37 passed)
• relevant Playwright specs (25 passed)
• final focused Playwright regressions (3 passed)

[chatgpt-codex-connector]

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