docs: removed outdated warning and enhanced tree component documentation

[laske185]

This pull request updates the documentation for the Tree component to improve clarity, consistency, and usability. The changes include refining descriptions, reorganizing content, and enhancing the keyboard navigation instructions.

Documentation Improvements:

• Removed the warning about accessibility testing and streamlined the description of the Tree component's functionality to make it more concise and user-friendly. (packages/components/src/components/tree/readme.md, packages/components/src/components/tree/readme.mdL5-R5)
• Enhanced the explanation of the Tree component's purpose and typical use cases, providing clearer examples and improving the readability of the text. (packages/components/src/components/tree/readme.md, packages/components/src/components/tree/readme.mdL51-R65)

Keyboard Navigation Enhancements:

• Rewrote the keyboard navigation section to improve clarity and align terminology with standard practices (e.g., using "Pos1" and "Ende" instead of "Home" and "End"). Added more precise descriptions of navigation behavior for each key. (packages/components/src/components/tree/readme.md, packages/components/src/components/tree/readme.mdL51-R65)

Closes #7813

The A11y and PO reviews will only take place after all other DoD steps have been completed by the Developer:

• Meaningful pull request title for the release notes
• Pull request is linked to an issue and all changes relate to the issue
• Tests to protect this code implemented (if applicable)
• Manual test performed successfully (if applicable)
• Documentation or migration has been updated (if applicable)

[github-actions]

Netlify Draft Deployment
URL: https://683eb732f80bc45c02beb6f0--kolibri-public-ui.netlify.app
Logs: https://app.netlify.com/projects/kolibri-public-ui/deploys/683eb732f80bc45c02beb6f0

[github-actions]

Hydration Benchmark Report (vs Baseline)

📊 Flop 5 Regressions

Component	Current	Baseline	Δ%	Result
kol-spin	6ms	5ms	+20.0%	🔻
kol-indented-text	7ms	6ms	+16.7%	🔻
kol-progress	7ms	6ms	+16.7%	🔻
kol-link-group	8ms	7ms	+14.3%	🔻
kol-textarea	32ms	28ms	+14.3%	🔻

📋 Show all results

Component	Current	Baseline	Δ%	Result
kol-abbr	18ms	18ms	0.0%	➖
kol-accordion	67ms	63ms	+6.3%	🔻
kol-alert	21ms	21ms	0.0%	➖
kol-avatar	10ms	10ms	0.0%	➖
kol-badge	31ms	32ms	-3.1%	➖
kol-breadcrumb	15ms	15ms	0.0%	➖
kol-button	45ms	45ms	0.0%	➖
kol-button-group	6ms	6ms	0.0%	➖
kol-button-link	45ms	44ms	+2.3%	➖
kol-card	11ms	11ms	0.0%	➖
kol-details	57ms	57ms	0.0%	➖
kol-drawer	8ms	8ms	0.0%	➖
kol-form	8ms	9ms	-11.1%	✅
kol-heading	10ms	10ms	0.0%	➖
kol-icon	8ms	8ms	0.0%	➖
kol-image	5ms	5ms	0.0%	➖
kol-input-checkbox	30ms	30ms	0.0%	➖
kol-input-color	30ms	28ms	+7.1%	🔻
kol-input-date	36ms	34ms	+5.9%	🔻
kol-input-email	33ms	32ms	+3.1%	➖
kol-input-file	27ms	26ms	+3.8%	➖
kol-input-number	29ms	29ms	0.0%	➖
kol-input-password	30ms	31ms	-3.2%	➖
kol-input-radio	23ms	22ms	+4.5%	➖
kol-input-text	33ms	34ms	-2.9%	➖
kol-link	41ms	40ms	+2.5%	➖
kol-link-button	41ms	40ms	+2.5%	➖
kol-logo	4ms	4ms	0.0%	➖
kol-modal	6ms	6ms	0.0%	➖
kol-nav	10ms	9ms	+11.1%	🔻
kol-pagination	68ms	62ms	+9.7%	🔻
kol-popover-button	50ms	46ms	+8.7%	🔻
kol-quote	6ms	6ms	0.0%	➖
kol-select	31ms	31ms	0.0%	➖
kol-skip-nav	7ms	7ms	0.0%	➖
kol-split-button	51ms	49ms	+4.1%	➖
kol-table-stateful	17ms	16ms	+6.3%	🔻
kol-table-stateless	15ms	14ms	+7.1%	🔻
kol-tabs	9ms	8ms	+12.5%	🔻
kol-toolbar	6ms	6ms	0.0%	➖
kol-tree	9ms	8ms	+12.5%	🔻
kol-tree-item	45ms	44ms	+2.3%	➖
kol-version	40ms	39ms	+2.6%	➖