fix: restore run_scan.py and skip BCC tests without bcc

[kramlipi]

Summary

CI Test Suite was red on ubuntu (3 failed / 551 passed). Root causes:

1. scripts/run_scan.py referenced by action.yml and test_run_scan_script_exists was missing — restored a composite-action helper that builds crucible scan from CRUCIBLE_* env vars.
2. TestLinuxBCCIntegration required BCC on every Linux runner; GitHub-hosted images do not ship BCC. Skip when BCC_AVAILABLE is false (matches the class docstring).

Failed run: https://github.com/crucible-security/crucible/actions/runs/29259410161

Verify

C:\Users\slc\AppData\Local\Python\pythoncore-3.14-64\python.exe -m pytest tests/test_github_action.py::test_run_scan_script_exists tests/test_ebpf_sidecar.py::TestLinuxBCCIntegration -q --tb=line

Local/verify gate applied before opening this PR.

This change was made by kramlip code-agent (verify-gated CI repair — customer-hosted / BYO LLM).

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