Restore contents:write permission for docs deploy (fix gh-pages 403)

[ChrisRackauckas-Claude]

Problem

The Documentation deploy fails on main. The docs build succeeds — the failure is in the deploydocs step, which pushes to gh-pages and gets a 403 / "Permission denied" (GITHUB_TOKEN cannot push).

Root cause

• This repo has no DOCUMENTER_KEY secret, so Documenter's deploydocs falls back to pushing to gh-pages via GITHUB_TOKEN.
• The CI-centralization migration replaced the old docs job with a thin caller of SciML/.github/.github/workflows/documentation.yml@v1 and dropped the permissions: block from the caller docs job.
• The reusable workflow declares no workflow-level permissions, so for a uses: reusable-workflow job the caller job's permissions (now the default, read-only contents) flow through to the GITHUB_TOKEN used inside the called workflow. A read-only token cannot push to gh-pages → 403.

Fix

Add permissions: { actions: write, contents: write, statuses: write } to the caller docs job in .github/workflows/Documentation.yml. This restores the token-based deploy mechanism the repo depends on (no DOCUMENTER_KEY required). Mirrors the proven fix in SciML/OrdinaryDiffEqOperatorSplitting.jl#90 exactly.

  docs:
    name: "Documentation"
    permissions:
      actions: write
      contents: write
      statuses: write
    uses: "SciML/.github/.github/workflows/documentation.yml@v1"
    secrets: "inherit"

Verification

• YAML validated locally with python3 yaml.safe_load (parses; the docs job carries the three permissions).
• The deploy itself cannot be fully verified without a CI run on main (the gh-pages push only happens on a real main/tag run). The change is correct by matching the proven #90 pattern: it grants the caller job the same contents: write (plus actions/statuses write) that the reusable workflow needs to flow into the GITHUB_TOKEN.

This does not disable the docs check or set warnonly.

Please ignore until reviewed by @ChrisRackauckas

[ChrisRackauckas-Claude]

Superseded by SciML/.github#102, which sets permissions: contents: write in the centralized documentation.yml reusable itself — so no per-repo permissions block is needed once v1 is retagged. Closing this in favor of the central fix.