Remove hardcoded mod.zip dependency; dynamic zip selection and Gradle project root detection

[Copilot]

Workflows assumed a file named exactly mod.zip at repo root and a hardcoded mod_extracted/ project layout. This replaces all that with runtime discovery of both the zip and the Gradle project root.

Changes (applied uniformly across all three workflows)

Trigger

• paths updated from mod.zip → *.zip + input/*.zip

Zip selection & extraction

• shopt -s nullglob collects candidates from input/*.zip then *.zip; picks first (zips[0])
• Fails explicitly if no zip found
• Extracts to deterministic work/ directory

Gradle project root detection

• Searches work/ for Gradle files in priority order: settings.gradle → settings.gradle.kts → build.gradle → build.gradle.kts
• Takes the first sorted match, logs what was detected, fails explicitly if nothing found
• Writes result to GITHUB_ENV as PROJECT_ROOT

Build & artifact upload

• Build step: validates gradle is on PATH, prints version, then cd "$PROJECT_ROOT" && gradle build --no-daemon
• Artifact path updated from hardcoded mod_extracted/build/libs/*.jar → ${{ env.PROJECT_ROOT }}/build/libs/*.jar

Error handling

All failure modes (no zip, no project root, no gradle binary) now emit explicit messages and exit 1 under set -euo pipefail.

# Before
unzip mod.zip -d mod_extracted
# working-directory: mod_extracted; path: mod_extracted/build/libs/*.jar

# After
zips=( input/*.zip *.zip )
[[ ${#zips[@]} -eq 0 ]] && { echo "ERROR: No .zip file found" >&2; exit 1; }
unzip "${zips[0]}" -d work
# PROJECT_ROOT detected dynamically; path: ${{ env.PROJECT_ROOT }}/build/libs/*.jar

Java version and Gradle version pinning (per-workflow) are unchanged.