docs: add package setup and AI/direct client usage guides

[lemuelvdm]

New users currently encounter component-only source installation and developer-oriented references before finding the complete package and client workflow. This makes it unclear which extensions to install and how to connect a Joomla site.

Lead the README with the stable combined package and the fourth iteration of the MCP implementation, distinguished from release version numbers. Add two user guides:

• docs/GETTING-STARTED.md: Joomla prerequisites, package/plugin setup, canonical URL, API token and ACL, administrator areas, first reads, grants/plans/apply, JCB synchronization/jobs, console use and troubleshooting.
• docs/CLIENT-CONNECTIONS.md: PHP/Composer and Docker stdio launchers, Claude connections, direct Streamable HTTP, ChatGPT compatibility requirements, and a complete SDK tool-call example without an AI.

The guides distinguish the separate client and JCB installations, local console authority and remote token permissions. They document the current transport boundary: the PHP client provides stdio, while ChatGPT web needs a compatible reachable HTTPS MCP endpoint/authentication or a separately hosted adapter.

Validation: checked commands, settings, tool arguments and SDK signatures against current source; validated Markdown paths/anchors and XML changelogs; Bash examples pass bash -n. PHP examples were source-reviewed because PHP/Composer are unavailable in the editing environment; no live Joomla execution is claimed. Both changelogs contain matching pending documentation entries. Runtime and release configuration are unchanged.

Merge this PR before the coordinated README navigation PRs in joomla-mcp, mcp_client, mcp_plugin and mcp_webservices, which link to these new guides. The package repository's root README is generated by OctoJPack, so it is not manually edited.

Coordinated review PRs:

• joomla-mcp #51
• mcp_client #3
• mcp_plugin #5
• mcp_webservices #3