Update ConfigEditor for render strategies + editing language

[amoghbanta]

Summary

• Removed broken web_rendering.model and max_retries inputs (config key no longer exists after pipeline team's render strategies refactor)
• Added editable default_render_strategy input with placeholder from active config
• Added read-only render strategy summary showing available strategies with type badges (e.g. two_column [template], llm [llm])
• Made editing_language editable (was read-only display)
• Preserved render_strategies, section_render_strategies, default_render_strategy, and translation on save in both ConfigEditor and StoryboardSettingsSheet

Test plan

• pnpm typecheck passes
• pnpm test passes (330 tests)
• Open a book → Config tab → verify no "Web Rendering" input or "Max Retries" field
• Config tab shows editable "Editing Language" input with placeholder from global config
• Config tab shows editable "Default Render Strategy" input
• Config tab shows read-only render strategy summary with type badges
• Save config → book config.yaml gets editing_language and/or default_render_strategy if set
• Save config → existing render_strategies, section_render_strategies, translation preserved
• Storyboard settings save → preserves new config fields, no longer writes web_rendering