Pandion v0.4.0

Changelog

• 1a85bb4 feat: IDE Tier-2 — distributed debug-attach over the overlay (pandion debug) (#51)
• cb10adf feat: OS-keychain secret store for provider tokens (H6) (#47)
• 2af1978 feat: pandion cp — scp files to/from a node (host-key pinned) (#42)
• 05b0db8 feat: add Vultr, Linode/Akamai, and Scaleway providers (#48)
• 49c78d6 feat: down --dry-run + confirm, pandion code (IDE), cross-platform CI (M7) (#45)
• 0dac994 feat: per-node engine=docker in clusters (P0-2 complete) (#43)
• 5dd6f66 feat: structured audit trail of infra actions (L3) (#46)
• fcc46ec fix: Vultr user_data base64 + no-leak e2e teardown; roadmap note (#49)
• f685aa3 polish: actionable credential errors for Vultr + Scaleway (#50)
• f5490d0 release: v0.4.0 — 5 providers + IDE Tier-2 debug-attach (#52)