Add Flixa ACP agent

[raicdev]

Summary

• Add Flixa as an ACP Registry agent.
• Configure the public npm distribution at @deniai/flixa-zed@0.8.1.
• Add a 16x16 monochrome Flixa icon.

Validation

• Confirmed @deniai/flixa-zed@0.8.1 is available from npm.
• Confirmed the published package responds to the ACP initialize request.
• Validated the registry with build_registry.py --dry-run using the Flixa entry.