Add license headers to source files and re-enable linters in CI

[rolker]

License headers missing from source files

Both packages declare the BSD license in package.xml and the repo carries a LICENSE file, but the C++ sources and headers have no copyright/license header blocks.

Adding headers to every source file is too invasive for the onboarding batch (PR for #39), so it is deferred here per workspace ADR-0008.

Note: udp_bridge_interfaces wires ament_lint_auto/ament_lint_common, and the onboarding CI excludes linter-labeled tests (--ctest-args -LE linter) until this is fixed — same pattern as rolker/unh_marine_navigation#98. When picking this up:

• Add a standard BSD header block matching LICENSE to all .h/.cpp files
• Fix any other ament_lint_common findings (uncrustify/cpplint/xmllint)
• Re-enable linters in CI by dropping the --ctest-args/--pytest-args exclusions

Part of #39 (onboarding). Identified by the onboard-project skill.

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Authored-By: Claude Code Agent
Model: Claude Fable 5