ci: expose path filter decisions

[lmeyerov]

Summary

First slice for #1689. This is observability only:

• log changed files in the changes job
• print path-filter: key=value for every computed filter
• add a GitHub step-summary table with changed files and filter booleans

No filter pattern, job gate, matrix, or dependency behavior changes in this PR.

Why

The target run for #1689 showed the filter regex definitions but not the emitted booleans, which made CI over-trigger analysis harder than necessary.

Validation

• bash -n on the extracted changes shell block
• git diff --check
• dry-run of PR fix(test): networkx HITS test used a degenerate cycle graph (scipy-version flaky) #1686 paths confirmed python=true, gfql=false, docs=true

Stack: 1/3. Next: classifier-only filter outputs.