deprecate(UIPanel): mark as deprecated in favour of GuiPanel

[AmlanDalai]

Overview

The codebase contains two navigation panels - UIPanel and GuiPanel - that serve identical purposes. This duplication increases maintenance burden and creates ambiguity about which class should be used for future development.

Problem

UIPanel and GuiPanel both:

• Display the same navigation buttons (Select Filters, Feature Extraction, etc.)
• Manage the same sub-panels (FilterPanel, FeaturePanel, LearningPanel, etc.)
• Initialise the same managers (FeatureManager, ClassifierManager)

Maintaining two parallel implementations increases the risk of divergence and makes future UI improvements harder to apply consistently.

Changes

• Add @Deprecated annotation and @deprecated Javadoc tag to class and methods
• Reference GuiPanel as the canonical replacement in all deprecation notices
• Migrate layout from setLayout(null) to GridBagLayout for consistency with GuiPanel
• Remove System.out.println debug statements from constructor
• Add full Javadoc to all methods

Note

UIPanel is retained for backwards compatibility. No functionality has been removed. The deprecation signals intent to consolidate into GuiPanel in a future release.

[AmlanDalai]

Note on diff size

This PR makes the following distinct changes:

1. Added '@deprecated' annotation and '@deprecated' Javadoc — signals 'UIPanel' should be replaced by 'GuiPanel'
2. Migrated 'setLayout(null)' to 'GridBagLayout' — consistent with 'GuiPanel' refactor in PR refactor(GuiPanel): replace absolute layout with GridBagLayout for responsive UI #98
3. Removed 'System.out.println' debug statements
4. Added Javadoc to all methods

The large diff is due to layout restructuring. All button actions and functionality are identical to the original.

[AmlanDalai]

Closing this PR following mentor feedback. UIPanel is the newer
experimental implementation — this deprecation was based on an
incorrect understanding of the class hierarchy. Apologies for
the confusion.