fix: register event_blobs in conversation bundles

[pandego]

Description

Register event_blobs in the canonical conversation registry bundles used by fixtures and cxtx, and add a regression test that proves typed projection now surfaces the field.

What changed?

• added event_blobs at AssistantTurn tag 11 in cxtx/src/conversation_registry_bundle.json
• refreshed fixtures/registry/conversation-bundle.json to mirror the canonical v3 conversation bundle instead of the stale 4-field sample
• updated scripts/generate-fixtures.sh to copy the canonical bundle into fixtures so the two files stay aligned
• added nested_event_blobs_field_projects_in_typed_view coverage in server/tests/registry_projection.rs

Why?

Typed HTTP projection only exposes registered fields. Without tag 11 in the published conversation bundle, event_blobs stays hidden unless clients opt into unknown-field fallbacks.

How to test?

• cd server && cargo fmt --check
• cd server && cargo test --test registry_projection
• JSON-parse cxtx/src/conversation_registry_bundle.json and fixtures/registry/conversation-bundle.json

Checklist

• Tests pass locally (cargo test, go test ./..., pnpm test)
• Linters pass (cargo clippy, cargo fmt, golangci-lint run, pnpm lint)
• Documentation updated (if applicable)
• CHANGELOG.md updated (if user-facing change)
• Breaking changes documented (if applicable)
• No compiled binaries committed
• No secrets or credentials committed

Related Issues

Fixes #18

Additional Notes

I kept this scoped to registry publication and projection coverage. I did not try to register the full external Amplifier schema beyond the missing event_blobs field.