🎨 feat(style): setup MUI theme

[coyote2190]

Decision Record

As part of the frontend refactoring, we are progressively removing TailwindCSS in favor of a fully MUI-based design system.

Before migrating components, it was necessary to introduce a centralized theme to ensure visual consistency across the application.

This PR introduces the initial MUI theme setup (palette, typography, spacing) and establishes the foundation for future UI refactoring.

Closes to #1190

Changes

• 🎨 Add MUI theme configuration (palette, typography, spacing)
• ✨ Introduce design tokens structure
• ♻️ Wrap application with ThemeProvider
• 🧱 Prepare foundation for TailwindCSS removal
• 🔄 Migrate existing components to MUI (next PRs)

License Agreement

• I guarantee that I have the rights on the code submitted in this PR
• I accept that this contribution will be released under the terms of the MIT License

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

	Tests	Passed ✅	Skipped	Failed
Consul End-To-End Test Report	1 ran	1 passed	0 skipped	0 failed

• View Consul End-To-End Test Report

[github-actions]

	Tests	Passed ✅	Skipped	Failed
API End-To-End Test Report	23 ran	23 passed	0 skipped	0 failed

• View API End-To-End Test Report

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
22	0	0	22	100	2m18.960747s

Passed Tests

Name	⏱️ Duration	Suite
Create and Delete Personal Access Token	21.643 s	Account
Change Password	6.004 s	Account
Restore Password	5.060 s	Account
Create test role	5.709 s	Admin
Create test user	5.509 s	Admin
Log as test user	4.106 s	Admin
Login With Valid Credentials	4.081 s	Auth
Login With Invalid Credentials	3.828 s	Auth
Logout	4.744 s	Auth
Create new forwarder	5.420 s	Forwarders
Configure forwarder	5.523 s	Forwarders
Delete forwarder	5.032 s	Forwarders
Create new stream	5.190 s	Storage
Configure stream	5.351 s	Storage
Delete stream	4.955 s	Storage
View logs sent on default pipeline	7.271 s	Stream-Viewer
View logs sent via Syslog (RFC 5424)	7.308 s	Stream-Viewer
View logs sent via Syslog (RFC 3164)	7.254 s	Stream-Viewer
Watch logs	8.288 s	Stream-Viewer
Create new transformer	5.350 s	Transformers
Configure transformer	6.290 s	Transformers
Delete transformer	5.045 s	Transformers