refactor: restructure settings window with native macOS patterns

[datlechin]

Summary

• Consolidate 12 settings tabs into 8 (General, Appearance, Editor, Keyboard, AI, Terminal, Plugins, Account)
• Extract section components into Settings/Sections/ — thin tab composers + self-contained sections
• Fix native macOS anti-patterns: HStack → LabeledContent, inline Text(.caption) → .help() tooltips and Section(footer:), segmented picker → popup menu inside Form
• Remove dead EditorSettings.autoIndent (stored but never consumed by editor)
• Wire dead MCP settings (defaultRowLimit, maxRowLimit, queryTimeoutSeconds) to MCPToolHandler
• Reorder fields: most-used first, destructive actions last
• Clean up stale iOS project references to deleted files

Test plan

• Open Settings, navigate all 8 tabs — verify layout, no regressions
• Appearance tab: theme list + editor display correctly, mode picker works
• Editor tab: verify autoIndent toggle is gone, data grid settings work
• Terminal tab: MCP section renders correctly, enable/disable works
• Account tab: license info + sync toggles + linked folders all functional
• Hover over converted controls — verify .help() tooltips appear
• MCP: change default row limit in settings → query via MCP → verify new default applies