docs(skill): update release-pipeline for the eras model

[amondnet]

Summary

Brings .claude/skills/release-pipeline/SKILL.md back in line with scripts/lib/upstream-sources.ts
after #15, #21 and #24.

• Support section now describes eras instead of a single minimumVersion: a table of the two
  Spring Boot eras (3.3.0–<4.0.0 synthesized, >= 4.0.8 archive) with the component path and
  where each era's generated half comes from, plus why the eras are not contiguous (3.2 predates the
  component, 4.0.0–4.0.7 fall between them, 4.1.0 is an unpublished-artifact fact probed over the
  network rather than an era boundary).
• Detection section describes the actual gate — era membership, then requiredArtifactUrls +
  unpublishedArtifacts bounded at PROBE_CONCURRENCY, run by both detect-upstream-versions.ts
  and fetch-upstream.ts.
• "Going below the floor" became "A version outside every era", carrying ADR-0004's measurement
  (3.5.16's bare checkout: 350 unresolved attributes, 837 unresolved configprop:, 326 empty
  include-code::) as the bar a new era has to clear.
• New-project checklist moves componentPath / archiveClassifiers into eras.
• Notes the 3.x generated-appendix gap, the new scripts/lib/ modules, and two operational facts
  found while publishing boot-4.0.8 / boot-4.1.1: catalog pull requests conflict when two
  releases are open at once, and they get no ci.yml run because GITHUB_TOKEN-created pull
  requests do not trigger workflows.

Documentation only; no pipeline behavior changes.

---

Summary by cubic

Updates the release-pipeline skill doc to match the layout-era model in scripts/lib/upstream-sources.ts that replaced the per-project minimumVersion, and records two release-operations facts learned while publishing boot-4.0.8 / boot-4.1.1. Documentation only; no pipeline behavior changes.

Doc updates

• Support table now describes two eras — 3.3.0–<4.0.0 synthesized from the tag plus metadata jars, >= 4.0.8 from the Maven Central content archive — and explains why they are not contiguous (3.2 predates the component, 4.0.0–4.0.7 have no archive, 4.1.0 is a publication fact probed over the network).
• Detection section now describes the actual gate: era membership, then requiredArtifactUrls HEAD-probed via unpublishedArtifacts at PROBE_CONCURRENCY, shared by detect-upstream-versions.ts and fetch-upstream.ts.
• "Going below the floor" becomes "A version outside every era," with ADR-0004's measurement (3.5.16: 350 unresolved attributes, 837 unresolved configprop:, 326 empty include-code::) as the bar new eras must clear.
• New-project checklist moves componentPath and archive classifiers into eras; notes the 3.x generated-appendix gap and the new scripts/lib/ modules.
• Records that catalog pull requests conflict when two releases are open at once and get no ci.yml run because GITHUB_TOKEN-created pull requests do not trigger workflows.

^{Written for commit 2b64261. Summary will update on new commits.}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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