Add Workbook Connect to the catalog

[gronnerup]

Summary

Adds Workbook Connect, a Windows Excel add-in from Plainsight that loads database tables into a worksheet and writes inserts, updates, and deletes back to Fabric SQL Database, Fabric Warehouse, SQL Server, and Azure SQL. Submitted in #30; it meets the inclusion criteria (a publicly downloadable tool with Fabric SQL Database and Fabric Warehouse as first-class targets).

Closes #30

Changes

• Added src/content/tools/workbook-connect.md: category databases, type extension, source proprietary, pricing freemium, maintainer vendor, status ga.
• Added the cached favicon for www.workbookconnect.com and its entry in src/data/favicons.json.

Verification

• npm run build and npx astro check pass (0 errors, 0 warnings).

Notes

• Kept type extension as submitted, since the add-in runs inside Excel rather than as a standalone application; the submitter said desktop-app is also fine.
• Dropped the submitted databricks tag (not relevant to Fabric filtering) and added write-back, so the tags are excel, data-entry, master-data, validation, write-back.
• The body notes the user guide's caveat that a failed commit on Fabric Warehouse can leave earlier rows written, since that matters for how the tool is used against Fabric.