Fix path normalization to handle '.' and '..' components

[Copilot]

ls without arguments (passing "." to opendir) fails because to_absolute_path() concatenates "." with the current directory, producing unnormalized paths like /mnt/. that filesystem implementations reject.

Changes

• Added normalize_path(): Resolves "." and ".." components in absolute paths using a stack-based approach

  • Manual string parsing (no strtok) for thread safety
  • Exact buffer sizing to prevent overflows
  • Handles edge cases: multiple slashes, root boundaries, excessive ".."

• Modified to_absolute_path(): Now normalizes all paths before returning

Example

// Before: 
to_absolute_path(".", "/mnt") → "/mnt/."  // ❌ Fails in opendir

// After:
to_absolute_path(".", "/mnt") → "/mnt"    // ✅ Works

// Also handles:
to_absolute_path("..", "/mnt/sub") → "/mnt"
to_absolute_path("./a/../b", "/mnt") → "/mnt/b"

All existing tests pass. CodeQL clean.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Listing current directory does not work properly</issue_title>
<issue_description>Currently listing by ls (without an argument) does not work properly:

stm32f746xg@/> ls
[ERROR] Failed to open directory '.'
[ERROR] Failed to open directory '.'

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Listing current directory does not work properly #45

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