fix: deduplicate custom_logo insert in logo_slot at runtime

[ahmed-arb]

Summary

• When multiple insert operations target logo_slot with the custom_logo widget, MFEs render duplicate logos. This patch dedupes those inserts at runtime so only the first custom_logo insert survives.
• Also sets keepDefault = false on logo_slot so the default logo content is suppressed when the slot is configured.

Test plan

• Configure a deployment where logo_slot ends up with more than one custom_logo insert plugin (e.g. multiple plugins/slots stacking).
• Verify only one logo renders in MFE headers and no duplicates appear.
• Confirm single-insert deployments still render the expected logo unchanged.

🤖 Generated with Claude Code

[Faraz32123]

LGTM!