IONOS(build): fix JSON comparison in workflow cache detection

[Copilot]

• Resolves: dont rebuild already built apps #127 (comment)

Summary

Direct JSON string comparison in workflow conditions fails on formatting differences (whitespace, ordering) despite semantic equality.

Changes

Replace string comparison with count-based boolean flag:

• Add has-cached-apps output to prepare-matrix job
• Compute by comparing APPS_TO_BUILD_COUNT < APPS_CHECKED
• Update restore-cached-apps condition from string equality to boolean check

Before:

if: needs.prepare-matrix.outputs.apps-to-build != needs.prepare-matrix.outputs.external-apps-matrix

After:

if: needs.prepare-matrix.outputs.has-cached-apps == 'true'

TODO

• Replace JSON string comparison with robust check
• Test logic handles all scenarios (all cached, some cached, none cached)

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

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