fix(JournalTable): button label colors to match theme

[SteKoe]

This pull request introduces several improvements to the frontend codebase, focusing on theme configuration, UI component behavior, and ESLint rules for test files. The main changes include refactoring the theme setup for better maintainability, updating UI dropdowns for improved user experience, and adjusting ESLint settings to accommodate test and spec files.

Theme configuration improvements:

• Refactored the theme setup in index.ts by moving the PrimeVue theme initialization into a dedicated setupTheme function. This also changes the color definitions for the primary palette to use CSS variables directly (e.g., 'var(--main-50)' instead of 'rgb(var(--main-50))'), simplifying theme customization. (spring-boot-admin-server-ui/src/main/frontend/index.ts)

UI component enhancements:

• Added the append-to="self" attribute to the application, instance ID, and event type filter dropdowns in JournalTable.vue. This ensures that the dropdown menus are appended to their own component, improving positioning and avoiding potential display issues. (spring-boot-admin-server-ui/src/main/frontend/views/journal/JournalTable.vue) [1] [2] [3]

ESLint configuration updates:

• Updated ESLint configuration to turn off the vue/one-component-per-file rule specifically for test and spec files, allowing multiple components per file in those contexts. (spring-boot-admin-server-ui/eslint.config.mjs)

closes #5254