Add daily workflow for GitHub Skills-style workshop activity PRs

[Copilot]

This introduces a daily agentic workflow that proposes incremental workshop improvements as draft PRs in GitHub Skills tone, explicitly targeting skill-style activities (content) rather than agent skills. It also enables Copilot request auth for workflow execution.

• Workflow intent and trigger model

  • Adds .github/workflows/workshop-skill-activity-author.md
  • Runs on schedule: daily and supports workflow_dispatch with optional focus input
  • Skips opening duplicate work when an existing skill-activity PR is already open

• Write path and safety boundaries

  • Keeps the agent job read-only except copilot-requests: write
  • Routes repo mutations through safe-outputs.create-pull-request
  • Restricts write scope to workshop markdown (workshop/*.md, workshop/**/*.md)

• Prompt contract (content, not agent skill)

  • Requires exactly one meaningful workshop improvement per run
  • Enforces GitHub Skills-style instructional tone
  • Explicitly prohibits edits under .github/skills/** and creation of SKILL.md
  • Requires noop when no meaningful improvement is available

• Compiled workflow artifact

  • Adds .github/workflows/workshop-skill-activity-author.lock.yml generated from the source workflow

permissions:
  contents: read
  copilot-requests: write
  pull-requests: read
  issues: read

safe-outputs:
  create-pull-request:
    labels: [workshop, skill-activity, documentation]
    allowed-files:
      - "workshop/*.md"
      - "workshop/**/*.md"