Replace fkirc/skip-duplicate-actions in CI workflows

[rtibbles]

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Overview

Replace fkirc/skip-duplicate-actions in studio's five workflows following the Strategy in learningequality/.github#83.

Complexity: Low
Target branch: unstable

The Change

• containerbuild.yml: no required check, but the postgres and nginx builds have separate path lists. Replace pre_postgres and pre_nginx with one dorny/paths-filter job that has two named filters. Tag pushes (v*) should always run both builds.
• deploytest.yml, frontendtest.yml, pre-commit.yml, pythontest.yml: swap fkirc for dorny/paths-filter in pre_job. Gated jobs keep their job-level if.

Acceptance Criteria

• No workflow references fkirc/skip-duplicate-actions.
• Every path list keeps its current patterns.
• Required check names are unchanged, and the PR body states that no ruleset change is needed.
• The PR links one run where the gated jobs ran and one where they were skipped with every required check green (a run on the contributor's fork is acceptable).
• actionlint passes on every changed workflow.

AI usage

I used Claude Code to survey this repo's workflows and required checks, and to draft this issue. I chose the approach and reviewed it before filing.

[rtibblesbot]

Plan: Swap fkirc/skip-duplicate-actions for dorny/paths-filter in studio's five gated workflows without changing which changes run which jobs.

• Swap the detect step in the three positive-list workflows
• Map pre-commit.yml's paths_ignore
• One detect job for containerbuild.yml
• Self-review the produced code

Assumptions — the issue did not settle these; say so if one is wrong.

• "Keeps its current patterns" means same matched files, so pre-commit uses !**/*.po/!**/*.json; literal !**.po would lint nested .po/.json-only PRs.
• Dropping fkirc-only actions: read from three workflows is safe; if a step needs it, that job 403s in the fork run.
• paths-filter runs on tag pushes (nutritionfacts#91, unmerged); if it errors on a tag ref, both release builds skip — the fork tag push checks this.

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@rtibblesbot's comments are generated by an LLM, and should be evaluated accordingly

How was this generated?

• Implemented code following the pre-approved plan using test-driven development (red-green-refactor)
• Ran the project's full test suite and linter before committing
• For UI changes: captured live screenshots to verify rendering
• For backend changes: verified with example API/CLI output