Add Posnic to the tool directory

[sridharkalaibala]

What does this PR do?

Adds Posnic to data/tools.json as an open-source POS and billing software entry in the E-commerce category.

Posnic links:

• Website: https://posnic.io/
• Source: https://github.com/Posnic/POS

The entry keeps the tone factual and includes a caveat that Posnic is a young open-source project with a small public GitHub community.

Related Issues

N/A

Validation

• Parsed data/tools.json with Node and confirmed the posnic entry is present.
• Validated every JSON file under data/ with jq empty.
• Ran git diff --check.
• Ran npm --prefix docs ci.
• Ran npm --prefix docs run build; Next.js build and Pagefind indexing completed successfully. Generated Pagefind artifacts were not committed so the PR stays focused on the source data.

Note: npm ci reports existing upstream audit warnings and an allow-scripts warning for sharp; no dependency changes are included in this PR.

Checklist

• I've read the CONTRIBUTING.md guide.
• This adds a new tool entry in data/tools.json using the existing schema style.
• This maintains a neutral, fact-based tone when making pros/cons edits.