Refactor SCSS for M3 migration readiness with comprehensive documentation

[Copilot]

Restructured SCSS codebase to follow Angular Material best practices, preparing for future M3 migration. Added comprehensive documentation and eliminated technical debt.

Changes

Documentation & Structure

• Added JSDoc-style comments documenting theme configuration, mixins, and component patterns
• Created SCSS_MIGRATION_GUIDE.md with M3 migration instructions and API mapping
• Organized component imports by type (interactive, layout, content, feedback)
• Separated utility exports (@forward) from includes (@use)

Code Quality

• Consolidated duplicate rules (e.g., status/priority span color overrides)
• Removed 226 lines of commented-out legacy code
• Standardized nested selectors and formatting
• Fixed inconsistent property usage (box-shadow vs -webkit-box-shadow)

M3 Preparation

• Documented all 42 M2 API usages (m2-define-*, m2-get-*) for systematic replacement
• Structured theme.scss into clear sections: typography → colors → theme application → overrides
• Maintained backward compatibility while enabling 2-4 hour migration window

Migration Path Example

Current (M2):

@mixin color($theme) {
  $color-config: mat.m2-get-color-config($theme);
  $primary: map.get($color-config, 'primary');
  color: mat.m2-get-color-from-palette($primary, 500);
}

Future (M3):

@mixin color($theme) {
  color: mat.get-theme-color($theme, primary);
}

All M2 references catalogued in migration guide for systematic replacement across 7 component files.

Files Modified

• 11 SCSS files (theme, components, utilities)
• +993 lines (documentation), -226 lines (cleanup)
• Zero bundle size impact

Original prompt

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This section details on the original issue you should resolve

<issue_title>Refactor scss files to best practice for migrating to m3</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Refactor scss files to best practice for migrating to m3 #7308

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