Stabilize publication infrastructure: scope detection guard, Pages fallback, release dedup, metadata corrections

[Copilot]

Several compounding fragilities in the publication pipeline cause predictable failures under common conditions (force-push, docs-only commits, concurrent release triggers). This PR addresses the highest-impact issues identified in the publication system audit.

Workflow fixes

• publication.yml — missing git cat-file guard (S1)
  detect-scope was calling git diff against BASE without verifying reachability. Added the same guard already present in pages.yml:

  if [[ -n "${BASE}" ]] && ! git cat-file -e "${BASE}^{commit}" 2>/dev/null; then
    echo "Base commit ${BASE} is unavailable in checkout history; falling back to full repository scan."
    BASE=""
  fi

  Eliminates fatal: bad object on force-push, rebase, and first-push scenarios.

• pages.yml — hard-fail on missing fallback PDFs (M1)
  When a build is skipped, docs/reflector.pdf doesn't exist (it's transient, never committed). The sync and verify steps were unconditionally asserting its presence. Both steps now treat absent fallback PDFs as a warning — Pages serves the last deployed version instead of failing the deployment. PDFs are still required when the build actually ran.

• release-paper.yml — release creation race condition (M2)
  Both publication.yml and release-paper.yml (triggered by tag push) could race to create the same GitHub Release. Added a pre-check that skips creation if the release already exists:

  if gh release view "${TAG}" >/dev/null 2>&1; then
    echo "Release ${TAG} already exists. Skipping."
    echo "skip=true" >> "$GITHUB_OUTPUT"
  fi

Metadata corrections

• .zenodo.json — "license": "mit" → "license": "apache-2.0" (correct SPDX identifier)
• docs/index.html — hardcoded v0.0.1 updated to v0.1.1

Deliverables

Per issue requirements, three documentation artifacts generated:

• audits/publication-infrastructure-audit-followup.md — resolution status for all 12 audit findings
• audits/publication-artifact-inventory.json — artifact lifecycle with producer/consumer/ownership/persistence
• docs/publication-workflow-map.md — canonical workflow reference: ownership, trigger conditions, deployment/release/sync flows, scope detection table, coupling points

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