Refactor builder panels: modularize controls and split left/right panels

[a5sh]

Motivation

• Reduce duplication and bloat in the builder UI by extracting reusable control primitives and splitting large monolithic panel files into focused modules.
• Improve maintainability and consistency between the simple and advanced builder experiences by providing a shared panel-switching API and a single simple/advanced toggle.
• Prepare the codebase for future UI/UX improvements (per-panel advanced editor, easier tests, and smaller reviewable units).

Description

• Extracted shared builder UI primitives into src/components/builder/components/controls/BuilderControls.tsx (Section, SliderRow, ToggleRow, SegmentedRow, TextInputRow, SelectBox, ColorRow) and replaced many inline copies in PropertyPanel and LayerPanel with these controls.
• Split the left and right panel surfaces into individual modules under src/components/builder/components/panels/ (left/SourcePanel, left/LayersPanel, left/PosterPanel, right/BadgesPanel, right/SelectionPanel) and added AdvancedPanelHost + AdvancedPanelList to drive the advanced left rail.
• Added a compact PanelSwitcher (components/layout/PanelSwitcher.tsx) and a BuilderModeToggle (components/layout/BuilderModeToggle.tsx) and wired the header to use the new mode toggle instead of the previous support CTA.
• Updated LayerPanel, PropertyPanel, Inspector, AdvancedBuilderApp, and the simple BuilderApp composition to load the new per-panel modules (desktop sidebars and mobile sheet), and introduced a forcedPanel prop so the same panel can be hosted in different layouts without duplicating logic.

Testing

• Ran a production build with npm run build, which completed successfully and produced static pages (build ✓).
• Ran unit test runner with npm test; Vitest returned “No test files found” (exit indicates no tests were executed).
• Ran type checking with npm run typecheck; TypeScript reported remaining type errors unrelated to the refactor (pre-existing repo type debt in admin analytics, command palette/preview canvas unused symbols, and a few other files), so typecheck did not fully pass.

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Codex Task

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	posterium-frontend	ee5a418	Commit Preview URL Branch Preview URL	May 08 2026, 06:17 PM