docs(wasm): fix outdated api references in readme (fixes #42)

[kalwalt]

PR Summary

• Type: Documentation fix
• Files changed: crates/wasm/README.md
• Impact: Resolves user confusion about the WASM API.

Detailed Description

This PR addresses #42, where the npm README for @webarkit/purecv-wasm contained outdated API references that caused runtime errors for users.

The following corrections were made to the documentation:

1. Replaced PureCvMatrixU8 with the actual exported Mat class.
2. Updated Mat.create() to the correct Mat.new() syntax.
3. Changed camelCase function names (e.g., gaussianBlur) to the modern snake_case WASM bindings (gaussian_blur).
4. Replaced hardcoded integer values with proper imports (CV_8UC3 and BORDER_DEFAULT).
5. Updated the API coverage section to reflect the snake_case naming conventions (e.g., absdiff, cvt_color, morphology_ex).
6. Fixed the import path (dist-std/purecv_wasm.js).

Review Checklist

• Code examples are copy-pasteable and syntactically correct.
• Referenced constants (CV_8UC3, BORDER_DEFAULT) are properly imported.
• Memory management section accurately references Mat instead of PureCvMatrixU8.
• API coverage list uses up-to-date snake_case names.

Risk Assessment

• Risk Level: Lowest
• Mitigation: This is solely a documentation change targeting the WASM package README. It does not affect the actual purecv Rust or WASM code execution.

Test Coverage

• N/A (Documentation only)

Size Recommendations

• Status: Excellent. This PR is small, atomic, and addresses a single issue directly.

Fixes #42