Seed the shared CI tools

Split out of the four repos per weblib-archive#44. All three files were
byte-identical across every repo at this moment, which will not stay true --
they converged only because four twin PRs landed within hours today, and
report_job_log.py had already drifted once before that.

Taken from weblib-archive, verified identical to every other copy first:

  with-nixpkgs.sh       ca43fa20  (cfbypass, archive, fs)
  report_job_log.py     aaef8f62  (cfbypass, archive)
  sync_blocked_label.py e6ddb21d  (all four)

action.yml is included so the `uses:` question can be re-measured now the repo
is public; it did not work while private.

Co-authored-by: bit <bit@das-labor.org>

action.yml

@@ -0,0 +1,22 @@
+# Makes the shared tools available to a workflow and reports where they are.
+#
+# Whether this is usable at all depends on `uses:` resolving a repo on this
+# Gitea, which is instance configuration rather than something a repo controls.
+# Measured on weblib-archive#44 while weblib-ci was still private: it did not
+# work. Re-measured once the repo was public - see the README for the outcome
+# and for the fallback, which is a plain clone and always works.
+name: weblib CI tools
+description: Shared CI scripts for the weblib repos.
+
+outputs:
+  path:
+    description: Directory holding with-nixpkgs.sh and the python tools.
+    value: ${{ github.action_path }}
+
+runs:
+  using: composite
+  steps:
+    - shell: bash
+      run: |
+        echo "weblib-ci tools at ${{ github.action_path }}"
+        test -f "${{ github.action_path }}/with-nixpkgs.sh"