CAMEL-23565: CI skip Scalpel analysis for root pom.xml changes

[davsclaus]

Summary

• Skip Scalpel POM analysis when only the root pom.xml changes (not parent/pom.xml or module-level pom.xml files)
• The root pom.xml contains build-infrastructure config (license plugin, checkstyle, etc.) that doesn't affect module compilation or test behavior
• Without this filter, Scalpel reports every module as affected because they all inherit from the root POM, causing CI to test the entire project unnecessarily (as seen in PR camel-tui: Add --record option and demo tape recordings #23364)

Changes

• .github/actions/incremental-build/incremental-build.sh: Changed Scalpel trigger condition to only fire when a subdirectory pom.xml changes — extracts file paths from the diff with sed and checks for paths containing at least one directory level before pom.xml
• .github/CI-ARCHITECTURE.md: Document the root pom.xml exclusion behavior

Test plan

• Verified grep logic handles all edge cases:
  • Root pom.xml only → Scalpel skipped
  • parent/pom.xml → Scalpel runs
  • Module pom.xml (e.g. components/camel-kafka/pom.xml) → Scalpel runs
  • Root + module pom.xml → Scalpel runs
  • No pom.xml changes → Scalpel skipped
• CI run on this PR should only test CI-related files (not every module)

Claude Code on behalf of Claus Ibsen

[github-actions]

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