Fix case-sensitive file extension matching in PlainTextDecoder detection

[coderabbitai]

Problem

Currently, file type detection uses case-sensitive extension matching via fileName.endsWith(ext) without normalizing the filename to lowercase. This means files like "SERVER.LOG" won't be detected as Plain Text files on case-sensitive filesystems (Linux), while they would work on case-insensitive filesystems (Windows).

Expected Behavior

File extension matching should be case-insensitive across all platforms for consistent user experience.

Suggested Solution

Update tryCreateDecoderByExtension in src/services/LogFileManager/decodeUtils.ts to normalize the filename and/or extensions to lowercase before performing the endsWith check:

• Use fileName.toLowerCase().endsWith(ext.toLowerCase())
• Update any related extension comparison logic

Context

This issue was identified during review of PR #370 which adds PlainTextDecoder support.

Backlinks:

• PR: feat(decoder): Add PlainTextDecoder to decode plaintext log files (resolves #271). #370
• Discussion: feat(decoder): Add PlainTextDecoder to decode plaintext log files (resolves #271). #370 (comment)
• Requested by: @junhaoliao