Make export/import unconditional and drop its setting

[scgopi]

What

Export/import of loops is now always available. GraphcodeSettings.sharesLoops is gone, along with the "Export and import loops" toggle in Settings.

Why

The switch has defaulted to on since 0.1.40. Every surface behind it is a right-click menu item that does nothing until deliberately clicked — nothing runs, nothing is spent — so the toggle only offered a way to hide working verbs from yourself.

Changes

Area	Change
GraphcodeSettings	property, init parameter and decode migration removed
SettingsView	toggle + its caption removed
Canvas / overview / sidebar menus	five if sharesLoops gates unwrapped
AppSidebarView	stored flag dropped; the segfault note it carried moved to offersCodespaces, which needs it for the same reason
graphcode-cli	requireLoopSharing() and its dispatch removed
SessionBriefing	the "stay off until enabled in Settings" caveat dropped from the export/import bullet
Tests	three assertions repointed to other settings; briefing test now checks the node import verb

A settings file that still records "sharesLoops": false is ignored — that is what enabling by default means here.

Verification

Check	Result
xcodebuild -scheme graphcode build	✅ 0 errors
-scheme graphcode-cli / -scheme graphcoded	✅ 0 errors
Tests	✅ 1537 tests in 160 suites passed
swiftlint lint	✅ 0 errors
swift format lint --strict	✅ clean

🤖 Generated with Claude Code

https://claude.ai/code/session_013EUE64JZc1QUodfL8LnPkK