feat(app): refine projects and extension settings

[jhe009809-hue]

Summary

• Reorganized sidebar conversations into project and ungrouped sections, with consistent hover areas, collapse interactions, icon sizing, alignment, and stroke weight.
• Added managed local project creation when no source folder is selected, including the redesigned project dialog and conversation engine selection states.
• Redesigned the Settings Extensions experience with responsive, centered layouts shared across embedded and standalone entry points.
• Updated plugin and skill libraries with unified navigation, filters, cards, installed-plugin previews, overflow controls, localized errors, and detail actions.
• Standardized Settings typography, spacing, buttons, tabs, inputs, selects, borders, radii, and focus states.
• Refreshed extension and brand assets, including curated third-party icons and the current iPolloWork logo.
• Improved embedded Extensions behavior by preserving sidebar restoration while removing redundant close and right-panel controls.
• Refined Composer selector and disabled-action styles for clearer visual consistency.
• Preserved the latest main plugin workspace and navigation capabilities while resolving merge conflicts.

Testing

• 75 focused application tests passed.
• 26 desktop workspace-store tests passed.
• Application and Electron TypeScript checks passed.
• Maintainability audit passed with no errors.
• Fraimz validation passed for project creation, responsive embedded Extensions, and the complete plugin/skill library flow.