Several improvements and additions to documentation, workflow configuration, and project metadata

[rafageist]

This pull request introduces several improvements and additions to documentation, workflow configuration, and project metadata. The most significant changes are the addition of detailed documentation for the template engine, updates to GitHub workflow triggers, and enhancements to project packaging and release processes.

Documentation additions and improvements:

• Added comprehensive introductory and conceptual documentation in the docs/01 Introduction.md and related files, covering engine behavior, dialect system, core operations, install/upgrade instructions, goals, reasons, best practices, and usage of the div class. This greatly expands the project’s documentation for new and existing users. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
• Added a new chapter docs/02 Template Features.md and a section on syntax understanding in docs/02.01 Understanding the syntax.md, outlining all supported template features and block types. [1] [2]

Workflow and automation enhancements:

• Updated GitHub Actions workflows (phpstan.yml, tests.yml) to add manual trigger support with workflow_dispatch, and removed push triggers to master branch for improved control and flexibility. [1] [2]
• Modified release workflow to reference release notes from the releases directory instead of docs/ChangeLog/releases, and updated the release name to include "Div PHP Template Engine" for clearer identification. [1] [2]

Packaging and project metadata:

• Added .gitattributes entries to mark various directories and files as export-ignore for cleaner package exports.
• Updated composer.json to bump the project version from 6.1.2 to 6.1.3.

Miscellaneous:

• Removed a redundant line from the end of README.md for clarity.