ci: bundle ci.yml improvements (sccache pin, cache monitoring, conan.lock, CLAUDE.md sync, composite action)

[mvillmow]

Summary

• ci: pin mozilla-actions/sccache-action to a SHA #350: Pin mozilla-actions/sccache-action to commit SHA 9e7fa8a12102821edf02ca5dbea1acd0f89a2696 (v0.0.10) in ci.yml, build-and-test.yml, and profiling-weekly.yml to prevent supply-chain attacks via mutable tags
• ci: unify Conan cache step into install-build-deps composite action #353: Add cache-conan input to .github/actions/install-build-deps/action.yml composite action; remove 3 duplicate actions/cache@v5 Conan steps from ci.yml and 1 from build-and-test.yml, replacing them with cache-conan: 'true'
• ci: add cache size monitoring and eviction alerting #351: Add "Monitor GitHub cache usage" step to the summary job that queries the GH Cache API and emits ::warning:: when usage exceeds 7 GB
• Generate and commit a conan.lock file for reproducible audits #247: Add conan lock create check step to the quality job in ci.yml; commit initial conan.lock; add just update-conan-lock target to justfile
• Automate CLAUDE.md tree sync via CI to prevent stale docs #232: Add just check-docs-tree justfile target that diffs find tests/ -maxdepth 1 -type d against the CLAUDE.md Test Structure block; wire it into the quality job

Test plan

• CI run on this PR passes the quality job (formatting, docs-tree, conan-lock checks)
• Verify sccache-action references use the SHA not the floating tag
• Verify no duplicate Cache Conan packages steps exist in workflow jobs
• Verify summary job emits cache usage line in logs
• Verify conan.lock is present at repo root

Closes #350
Closes #351
Closes #232
Closes #247
Closes #353

🤖 Generated with Claude Code

[github-actions]

✅ Dependency Audit

Severity	Count
Critical	0
High	0
Medium	0
Low	0

See the Security tab for detailed findings.

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Workflow: Dependency Audit

[github-actions]

Security Scan Results

• ❌ Secret Scanning: Potential secrets found
• ✅ SAST: Completed (check Security tab for details)
• ✅ Dependency Scanning: Completed
• ✅ C++ Static Analysis: Completed
• ✅ Docker Image Scanning: 0 high, 22 medium vulnerabilities (acceptable)

Recommendations

• Review findings in the GitHub Security tab
• Check artifact uploads for detailed reports
• Address critical Docker vulnerabilities immediately

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Workflow: Security Scanning