feat(standard): add §7 Shell Environment — v1.22

[UnbreakableMJ]

Summary

• Adds §7 Shell Environment — codifies Nushell, Ion, Brush, and Bash as four equally first-class shell environments
• §7.1 Script Portability Policy: POSIX-compatible scripts by default; Nushell/Ion native variants where shell-native idioms are needed; Bashisms prohibited in shared scripts
• Renumbers current §7–§14 → §8–§15 throughout the document (section headers + all in-text cross-references)
• Adds §7 shell compliance bullet to the checklist (now §15)
• Adds spacecraft-cli-shell + spacecraft-cli-preference row to Skill Cross-References

Test plan

• Section headers §7–§15 all present and correctly ordered
• No stale §7 — Privacy / §8 — Key Bindings / §9 — Color Palette references in live content
• §12.2.1 / §13.2.1 cross-references are consistent throughout Date/Time section
• Version is 1.22, date is 2026-06-18 in both frontmatter and masthead
• Compliance checklist has 16 bullets (was 15)

🤖 Generated with Claude Code