Replace wget with curl -fsSL, normalize downloads, and prep for IPv6

[MickLesk]

✍️ Description

This update introduces a full migration from wget and curl -s to curl -fsSL across the entire codebase, following best practices for reliability, security, and error visibility.

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✅ Key Changes

• 🔄 Replaced all wget calls with curl -fsSL or curl -fJL (where --content-disposition was needed)
• 🔁 Unified all curl -s, curl -sL and partial variants to curl -fsSL
• 🧠 Introduced smart filename handling for:
  • curl -o <file> (explicit target)
  • curl -O (autodetected filename)
• 🧼 Removed incorrect/ambiguous uses like wget -qO- ... -O file
• 🧾 Replaced inline usages such as:
  • bash -c "$(wget ...)" → bash -c "$(curl -fsSL ...)"
  • source /dev/stdin <<< $(wget ...) → $(curl -fsSL ...)

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📁 Scope

Affected directories:

• /install
• /ct
• /misc
• VM setup scripts (/vm)
• api.func, build.func, and related helpers

File types:

• *.sh, *.bash, *.txt, and various install scripts

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🌐 IPv6 Preparation

• ⚙️ Enabled dual-stack / IPv6 endpoints for key services
• 🧪 Prepared frontend service call targets for native IPv6 support

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🧹 Other Improvements

• ✨ All affected scripts auto-formatted via VSCode Format Document
• 🧽 Cleanup of legacy logic and unused wget variants
• 🧾 Commented substitutions in some scripts for reviewer traceability

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🔗 Related PR / Issue

Link: #

✅ Prerequisites (X in brackets)

• Self-review completed – Code follows project standards.
• Tested thoroughly – Changes work as expected.
• [] No breaking changes – Existing functionality remains intact.
• No security risks – No hardcoded secrets, unnecessary privilege escalations, or permission issues.

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🛠️ Type of Change (X in brackets)

• 🐞 Bug fix – Resolves an issue without breaking functionality.
• ✨ New feature – Adds new, non-breaking functionality.
• 💥 Breaking change – Alters existing functionality in a way that may require updates.
• 🆕 New script – A fully functional and tested script or script set.
• 🌍 Website update – Changes to website-related JSON files or metadata.
• 🔧 Refactoring / Code Cleanup – Improves readability or maintainability without changing functionality.
• 📝 Documentation update – Changes to README, AppName.md, CONTRIBUTING.md, or other docs.

[michelroegl-brunner]

Looks good to me, i did not find anything obvious.