Feature/one liner install and landing page

[shodiBoy1]

Implemented changes:

• Added install.sh - a one-liner install script that detects OS/architecture, downloads the latest IDEasy release, and runs setup automatically. Works on macOS (Intel & ARM), Linux (x64 & ARM64), and Windows (via Git Bash).
• Added website/ - a landing page (index.html + style.css) with install instructions, copy-to-clipboard command, and an overview of IDEasy features.

This simplifies the current installation process from:

1. Go to GitHub releases page
2. Find the correct archive for your OS and architecture
3. Download it manually
4. Extract it
5. Run setup

To just:
bash -c "$(curl -fsSL https://raw.githubusercontent.com/devonfw/IDEasy/main/install.sh)"

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Checklist for this PR

• When running mvn clean test locally all tests pass and build is successful
• PR title is of the form #«issue-id»: «brief summary» (e.g. #921: fixed setup.bat). If no issue ID exists, title only.
• PR top-level comment summarizes what has been done and contains link to addressed issue(s)
• PR and issue(s) have suitable labels
• Issue is set to In Progress and assigned to you or there is no issue (might happen for very small PRs)
• You followed all coding conventions
• You have added the issue implemented by your PR in CHANGELOG.adoc unless issue is labeled
  with internal

[coveralls]

Pull Request Test Coverage Report for Build 23643849312

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 70.425%

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Totals
Change from base Build 23641462284:	0.02%
Covered Lines:	10799
Relevant Lines:	14726

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💛 - Coveralls