Plan summary step fails when a plan changes only outputs #33

Problem

The Plan summary step in .github/workflows/base.yml extracts a one-line summary from the saved
plan with:

line=$(grep -E 'No changes\.|Plan: ' /tmp/<env>.plan.txt)

GitHub Actions runs run: blocks under bash -e, so when grep matches nothing it exits 1 and
takes the whole step (and job) down.

A Terraform plan that changes only outputs prints neither Plan: nor No changes. — it prints
Changes to Outputs: — so any change that adds or edits outputs without touching resources fails
the plan workflow.

Seen in capture-managed:
https://github.com/kosli-dev/capture-managed/actions/runs/33159178074/job/98809231312

Proposed fix

Tolerate a non-matching grep and fall back to the Changes to Outputs: header, then to a generic
message, so the summary degrades gracefully instead of failing the run. has_changes is unaffected:
an outputs-only plan has no No changes. line, so it correctly reports true and the apply job
still runs.