feat(charm): add lipgloss styling with Slack brand colors under charm experiment

[srtaalej]

Changelog

Adds lipgloss-based output styling under the charm experiment flag, using a centralized Slack brand color palette shared across all CLI components, and migrates all direct Styler() usage to named style functions. 🦋

Summary

This PR introduces a centralized Slack brand color palette (colors.go) as the single source of truth for all styling across lipgloss, huh themes, and future bubbletea components

• Adds lipgloss-based styling to all CLI output functions (behind the charm experiment flag), alongside existing aurora styling
• Migrates all external Styler() call sites to use new style functions (Green(), Red(), Yellow(), Gray())
• Consolidates all legacy aurora code into one clearly marked block for easy removal when the charm experiment is permanently enabled

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

❌ Patch coverage is 28.30189% with 76 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.92%. Comparing base (c449532) to head (0c3d9d6).

Files with missing lines	Patch %	Lines
internal/style/style.go	24.13%	66 Missing ⚠️
internal/pkg/platform/activity.go	33.33%	4 Missing ⚠️
cmd/upgrade/upgrade.go	0.00%	2 Missing ⚠️
internal/pkg/apps/install.go	0.00%	2 Missing ⚠️
cmd/manifest/validate.go	50.00%	1 Missing ⚠️
internal/iostreams/printer.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #365      +/-   ##
==========================================
- Coverage   65.06%   64.92%   -0.15%     
==========================================
  Files         215      215              
  Lines       18179    18248      +69     
==========================================
+ Hits        11829    11847      +18     
- Misses       5254     5306      +52     
+ Partials     1096     1095       -1     

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