fix: preserve VFS cache during navigation refresh

[Stardust0831]

Summary

• add a pinned rclone v1.74.4 source patch with a cache-preserving vfs/refresh-swr RC capability
• keep directory snapshots readable during remote listing, discard cancelled/stale results, and serialize cache cleanup without blocking ancestor reads
• route passive navigation only through the custom capability while leaving manual refresh unchanged
• build and verify rclone v1.74.4-ssh-mountmate.1 natively on all six release targets
• prepare v0.6.0-alpha.6

Verification

• focused patched-rclone tests passed from a pristine upstream worktree
• focused go test -race passed
• patched rclone static build and version/capability checks passed
• Rust formatting, workflow YAML, provenance JSON, patch digest, shell syntax, and git diff --check passed
• independent Sol review found no remaining critical, important, or minor findings

Local Rust unit execution was blocked by missing WSL pkg-config/DBus development files; the GitHub Linux quality runner installs those dependencies and remains the authoritative full-workspace gate.

[coderabbitai]

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