fix(tui): read tool uppercase/mixed case image extensions

[alexyaroshuk]

fixes #10916

What does this PR do?

• Fixes the read tool (used in terminal/CLI) failing to read images with uppercase or mixed case extensions (.PNG, ., .pNG, .PnG etc.), showing 'canot read binary file' error
• Additionally fixes mixed case (ie Png, PnG, etc.) which were failing previously

The problem:

read frame.PNG, .Png, .pNG, etc. returned "Cannot read binary file" error
read frame.png worked fine
Bun's MIME type detection doesn't handle uppercase extensions correctly

The fix: Added extension-based image detection before MIME type detection:

Check file extension (case-insensitive)
Map extension to correct MIME type (png→image/png, jpg→image/jpeg, etc.)
Handle image immediately if extension matches

How did you verify your code works?

1. test suite: no regression
2. manual testing in dev, and in standalone executable: test.PNG, test.pNg, test.JPG all work correctly, no longer causing an error

Before:

After

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one potentially related PR:

PR #11312: fix(app): binary file handling in file view
#11312

This PR appears to be related as it also addresses binary file handling issues. However, it's focused on the file view in the app rather than the CLI/TUI read tool specifically. You should verify if this addresses the same underlying issue or if they're separate concerns.

The current PR #11333 is the primary match for your search terms, which is the PR you're currently checking (so not a duplicate of itself).