refactor(ci): composite actions instead of reusable workflows (Forgejo 11)

Forgejo 11.0.15 does NOT support reusable workflows (job-level `uses:` /
`workflow_call`): the call is silently dropped and no run is scheduled (verified
live — a same-repo and a cross-repo reusable call both produced zero runs, while
an equivalent inline job ran green). The working cross-repo reuse primitive here
is the COMPOSITE ACTION referenced by FULL URL (a short-form
`uses: olsitec/foundation/...@master` resolves against the runner's
DEFAULT_ACTIONS_URL = data.forgejo.org, not the local instance, and 404s; the
full-URL form `uses: https://forge.olsitec.net/olsitec/foundation/actions/<x>@master`
was verified green).

- Replace the four reusable-*.yml with composite actions under actions/:
  node-build, docker-build, lint, semantic-release-version (same logic + inputs).
- actions/README.md documents the pattern, the Forgejo-11 limitation, and the
  999_testing candidate coverage (C2/C3/C4 self-contained; C1/C5 blocked on the
  not-yet-published @olsitec package registry).
- ecosystem-selftest paths filter: actions/** (was reusable-*.yml).

The capabilities that need no external repo (semantic-release bump sequence,
eslint/yamllint gates) keep running green via ecosystem-selftest's inline jobs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

actions/semantic-release-version/action.yml

@@ -0,0 +1,71 @@
+# semantic-release-version — compute the next semver from conventional commits
+# (999_testing "semantic-release testing"). Composite action (see actions/node-build).
+# Mirrors the canonical GitLab template (olsitec/gitlab ci_templates/release-automation/
+# semantic-release.yaml): conventionalcommits preset + Olsitec's releaseRules, run as a
+# `--dry-run --no-ci --tag-format '${version}'` probe. Outputs the computed version.
+#
+#   jobs:
+#     version:
+#       runs-on: docker
+#       container: { image: foundation-ci:latest }
+#       outputs: { version: "${{ steps.sr.outputs.version }}" }
+#       steps:
+#         - uses: actions/checkout@v4
+#           with: { fetch-depth: 0 }   # REQUIRED: full history + tags
+#         - id: sr
+#           uses: https://forge.olsitec.net/olsitec/foundation/actions/semantic-release-version@master
+#
+# NOTE: dry-run version compute only (the part 999_testing checks + the GitLab
+# `generate-release-version` job). Publishing a Forgejo release is deferred (no
+# @semantic-release/forgejo analogue yet).
+name: semantic-release-version
+description: Compute the next semantic-release version (dry-run) from conventional commits.
+inputs:
+  branch:
+    default: master
+outputs:
+  version:
+    description: "next release version (empty if the commits warrant no release)"
+    value: ${{ steps.compute.outputs.version }}
+runs:
+  using: composite
+  steps:
+    - name: Write .releaserc.yaml (Olsitec conventionalcommits ruleset)
+      shell: bash
+      run: |
+        cat > .releaserc.yaml <<'EOF'
+        branches:
+          - name: ${{ inputs.branch }}
+        tagFormat: "${version}"
+        plugins:
+          - - "@semantic-release/commit-analyzer"
+            - preset: conventionalcommits
+              releaseRules:
+                - { breaking: true, release: major }
+                - { type: breaking, release: major }
+                - { type: feature, release: minor }
+                - { type: feat, release: minor }
+                - { type: fix, release: patch }
+                - { type: build, release: patch }
+                - { type: chore, release: patch }
+                - { type: ci, release: patch }
+                - { type: docs, release: patch }
+                - { type: perf, release: patch }
+                - { type: refactor, release: patch }
+                - { type: style, release: patch }
+                - { type: test, release: patch }
+              parserOpts:
+                noteKeywords: [ "BREAKING CHANGE", "BREAKING CHANGES" ]
+          - "@semantic-release/release-notes-generator"
+        EOF
+    - name: Compute next version (dry-run)
+      id: compute
+      shell: bash
+      run: |
+        out=$(semantic-release --dry-run --no-ci --tag-format '${version}' --branches "${{ inputs.branch }}" 2>&1 || true)
+        printf '%s\n' "$out"
+        ver=$(printf '%s\n' "$out" \
+          | grep -oiE 'next release version is [0-9]+\.[0-9]+\.[0-9]+' \
+          | grep -oE '[0-9]+\.[0-9]+\.[0-9]+' | tail -1)
+        echo "computed next version: ${ver:-<none>}"
+        echo "version=$ver" >> "$GITHUB_OUTPUT"