fix(browser): show directories with dots in Browser listings

[blakelinkd]

Summary

Fixes Browser directory classification so folders with dots in their names are not hidden.

This affects Disk paths and can also affect Cloud paths with dotted folder names.

What changed

• Added iron_is_directory(path) in base runtime for explicit directory checks.
• Updated base directory sorting (file_read_directory) to keep dotted directory names in folder ordering.
• Updated paint browser listing to classify entries with explicit directory checks instead of filename dot heuristics.

Repro

1. Open ArmorPaint.
2. Go to Browser -> Disk.
3. Navigate to a folder with dotted directory names (e.g. /home/blake/Downloads).
4. Verify folders such as Textures from cc0textures.com - Part 2 are visible.

Result

Dotted directories are now shown correctly in Browser listings.

Fixes #2024

[luboslenco]

It looks like this one is mixed with #2023. I pushed a commit at d028010 with help from this PR to address the directory handling. Many thanks!