Transform landing page from conceptual to functional Wandersteine directory platform

[Copilot]

This PR completely transforms the website content from a conceptual "future of trail stones" landing page to a functional directory platform for personal hiking stones (Wandersteine), as requested in the issue.

Key Changes

Content Transformation

The website now presents itself as a directory platform where users can:

• Discover personal hiking stones near them
• Add their own stones to the collection with photos and stories
• Track the journeys and movements of stones
• Share experiences within a community of stone collectors

Updated Sections

Hero Section

• Changed from "Die Zukunft der Wandersteine" to "Dein Verzeichnis für Wandersteine"
• Emphasizes practical functionality: discovering, collecting, and tracking stones
• Updated call-to-action buttons to focus on features and community

Features Section (formerly "Story")

• Replaced historical content about ancient trail markers
• Now showcases platform capabilities:
  • "Steine entdecken" - Find stones with photos and locations
  • "Sammlung erweitern" - Add your own discoveries
  • "Reisen verfolgen" - Track stone movements

Community Section (formerly "Vision")

• Focus shifted to building a living directory
• Emphasizes local discoveries and story sharing
• Updated platform features list to match directory functionality

About Pages

• Updated mission to reflect stone collection and community sharing
• Replaced conceptual vision with practical platform description
• Both German and English versions updated consistently

Technical Updates

• Site description updated in _config.yml
• Maintained bilingual support (German/English)
• Preserved existing styling and responsive design
• All content updates follow existing design patterns

The website now accurately represents the requested functionality: "ein Verzeichnis von persönlichen Wandersteinen, Fundorten und Fotos" where users can see stones near them, add their own, and track their journeys.

Fixes #3.

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