Fix bash 3.2 compatibility: case conversion syntax

[ai-tesi]

Summary

• Replace ${var^^} and ${var,,} with helper functions using tr

Problem

After merging #26, the install still fails on bash 3.2:

lib/functions.sh: line 59: ${level^^}: bad substitution

The ${var^^} (uppercase) and ${var,,} (lowercase) operators require bash 4+.

Solution

Add helper functions in lib/functions.sh:

_mt_uppercase() {
  echo "$1" | tr '[:lower:]' '[:upper:]'
}

_mt_lowercase() {
  echo "$1" | tr '[:upper:]' '[:lower:]'
}

Then replace all usages:

• ${var^^} → $(_mt_uppercase "$var")
• ${var,,} → $(_mt_lowercase "$var")

Changes

File	Replacements
lib/functions.sh	5 + helper functions
lib/prompt.sh	8

Testing

Tested on fresh macOS Tahoe VM (arm64) with bash 3.2.57.

Note

This is the second of potentially several PRs needed for full bash 3.2 compatibility. Remaining issues may include:

• mapfile in lib/service.sh (7 usages)
• declare -A associative arrays (if any critical paths use them)

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