feat: add allowedIgnoreCase option to no-html

[TKDev7]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

This PR adds a new allowedIgnoreCase option to the no-html rule to enable case-insensitive matching for HTML tag names against the allowed array. This addresses the issue where HTML tag names are case-insensitive by specification, but the rule was performing case-sensitive matching, leading to false positives.
For example, with allowed: ["DIV"] configured:

• Before: Only <DIV></DIV> was allowed, but <div></div> was reported as an error
• After: With allowedIgnoreCase: true, both <div></div>, <DIV></DIV>, and <DiV></DiV> are allowed

What changes did you make? (Give an overview)

• Implemented case-insensitive matching logic that converts both the allowed tags and found tag names to lowercase when allowedIgnoreCase is true
• Added test cases for case-insensitive scenarios and mixed case handling
• Added examples and explanation for the new option

Related Issues

Fixes #479

Is there anything you'd like reviewers to focus on?

[Copilot]

Pull Request Overview

This PR introduces a new allowedIgnoreCase option to the no-html rule to enable case-insensitive matching of HTML tag names against the allowed list, addressing HTML's case-insensitive nature.

• Adds allowedIgnoreCase boolean option for case-insensitive tag matching
• Implements lowercase conversion logic for both allowed tags and found tag names when the option is enabled
• Includes comprehensive test coverage for various case scenarios

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/rules/no-html.js	Implements the core logic for case-insensitive matching with new option schema and comparison logic
tests/rules/no-html.test.js	Adds comprehensive test cases covering valid/invalid scenarios for case-sensitive and case-insensitive matching
docs/rules/no-html.md	Documents the new option with examples showing case-insensitive behavior

[snitin315]

@TKDev7 Before starting work, please wait for the issue to be accepted. The team is still finalizing the solution approach, and you can find more details in the contributing guidelines.

[lumirlumir]

It mostly looks good to me. I’ve left a few comments regarding documentation cleanups.

[lumirlumir]

LGTM, Would like another review before merging.

[nzakas]

LGTM. Thanks!