Support case-insensitive pattern matching

[srbdev]

Problem

Currently, patterns are matched with exact case only. For example, TODO: is highlighted but todo: and Todo: are not.

Different codebases and developers use varying conventions:

• TODO: (uppercase - most common)
• todo: (lowercase)
• Todo: (title case)

Proposed Solution

Replace indexOf with a case-insensitive regex match:

const regex = new RegExp(value.pattern, 'gi');
let match;
while ((match = regex.exec(line)) \!== null) {
    // create range using match.index and match[0].length
}

This would match all case variations while preserving the original text.