docs: rewrite README to reflect rhiza-based implementation

[Copilot]

The README documented a deprecated sparse-checkout based implementation with obsolete inputs (source, automerge, test-mode). The actual action uses rhiza for template materialization.

Changes

README.md

• Replaced sparse-checkout documentation with rhiza workflow (uvx rhiza validate . → uvx rhiza materialize .)
• Updated inputs table: token, branch, commit-message, create-pr (removed deprecated parameters)
• Added prerequisites section explaining rhiza requirement
• Updated all examples to use current API
• Changed version references from @v1 to @main

.github/workflows/integration-test.yml

• Fixed test to use current inputs (removed source: '.github/template.yml' and test-mode: "true")

Current Usage

- uses: jebel-quant/sync_template@main
  with:
    token: ${{ secrets.GITHUB_TOKEN }}
    branch: sync/template-update
    commit-message: 'chore: sync template'
    create-pr: 'true'

The action now requires repositories to have rhiza configuration in place rather than specifying a template repository via YAML config.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• astral.sh
  • Triggering command: /usr/bin/curl curl -LsSf REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Write a new and accurate README</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Write a new and accurate README #20

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