Fix critical issues in install.sh script - syntax errors, shellcheck warnings, and add version detection fallback

[Copilot]

The install.sh script had multiple critical issues that prevented proper functionality and posed security risks. This PR addresses all identified problems and significantly improves the script's robustness with enhanced error handling.

Critical Issues Fixed

Syntax Error: Fixed a critical syntax error on line 88 where ${$arch} should have been ${arch}, which would have caused the script to fail when reporting unsupported architectures.

Architecture Detection: Completely rewrote the architecture detection logic to properly handle all cases:

• Fixed broken case statement logic that could leave arch variable empty
• Changed _x86_64 to _amd64 to match actual GitHub release assets
• Added support for both aarch64 and arm64 architecture names
• Added proper error handling for unsupported architectures

Checksum Verification: Re-enabled the previously commented-out checksum verification function:

• Fixed the checksum file name from waitfor_checksums.txt to checksums.txt to match actual release assets
• Improved error handling for checksum failures
• Enhanced security by validating download integrity

Version Detection Fallback: Implemented robust fallback mechanism for version detection failures:

• Instead of failing completely when version detection fails, the script now falls back to using GitHub's latest release URLs
• Uses the proper releases/latest/download/ URL format for fallback downloads
• Maintains full functionality including checksum verification with fallback URLs
• Ensures installation continues to work even when GitHub API is temporarily unavailable

Shellcheck Compliance

Resolved all 20+ shellcheck warnings and errors:

• Added proper quoting around all variables to prevent word splitting and globbing attacks
• Replaced indirect exit code checks ([ "$?" = "0" ]) with direct command tests (if command; then)
• Removed unused variables (has, hasCurl, hasTar)
• Fixed POSIX compliance issues by replacing == with = for string comparisons
• Improved command chaining and error propagation

Security & Robustness Improvements

• Variable Quoting: All variables are now properly quoted to prevent injection attacks
• Error Handling: Added comprehensive error handling for download and extraction operations
• Platform Support: Added proper detection and error messages for unsupported platforms
• Input Validation: Enhanced validation of system information before proceeding
• Network Resilience: Script gracefully handles network issues and API unavailability

Validation

The updated script passes:

• All shellcheck tests with zero warnings/errors
• Bash syntax validation
• Architecture detection tests for supported and unsupported platforms
• URL construction validation against actual GitHub release assets
• Live testing of version detection and asset accessibility
• Fallback testing to ensure latest release downloads work when version detection fails

The script now provides a secure, robust installation experience with clear error messages and proper handling of edge cases, including network issues that may prevent version detection.

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[Copilot]

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