Fix settings form state ownership

[skyfallwastaken]

Summary of the problem

Settings controls mutated nested Inertia props directly, leaving editable state without a clear local owner or an explicit resynchronisation path when Rails returned fresh props.

Describe your changes

Editors, Notifications, Privacy and Slack & GitHub now bind through minimal local scalar state that resynchronises from the corresponding user prop. Editors continues to derive the goals control state from the editable display style. Browser coverage verifies dependent state and restoration after a rejected update.

Appearance keeps its overrideable derived theme value because it already follows prop updates without mutating the user prop.

Screenshots / Media

No visual changes.

[Copilot]

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[greptile-apps]

Greptile Summary

The PR moves editable settings values from direct mutation of Inertia props into locally owned Svelte state that resynchronizes when fresh server props arrive.

• Adds local scalar state for editor, notification, privacy, and Slack preferences.
• Continues deriving goal-control availability from the editable editor display style.
• Adds browser coverage for dependent editor controls and restoration after a rejected update.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
app/javascript/pages/Users/Settings/Editors.svelte	Replaces direct prop mutation with synchronized local state and derives goal availability from the editable display-style value.
app/javascript/pages/Users/Settings/Notifications.svelte	Moves the weekly-summary preference into locally owned state synchronized from fresh user props.
app/javascript/pages/Users/Settings/Privacy.svelte	Moves the public-stats preference into locally owned state synchronized from fresh user props.
app/javascript/pages/Users/Settings/SlackGithub.svelte	Moves the Slack-status preference into locally owned state synchronized from fresh user props.
test/system/settings/editors_settings_test.rb	Verifies dependent checkbox disabling and restoration of server values following a rejected settings update.

_{Reviews (2): Last reviewed commit: "Preserve settings state during SSR" | Re-trigger Greptile}