[flemming-n-larsen]

Summary

• Prepare the browser-form client changes as rumble-client 0.3.0.
• Remove the obsolete “battle execution is not available yet” message after successful configuration validation.
• Keep the browser submission flow in the release changelog and set the release version.

Verification

• ./gradlew.bat --no-configuration-cache clean test passed.
• Built the container image from this branch with Tank Royale commit 9c25770c02671d1f9d941aad312013562a441427.
• On Windows 11, PowerShell 7.6.7, Docker Desktop Engine 29.7.2 (linux/amd64), the image passed runtime check, ranked validation, catalog sync, one 1v1 battle, and credential-free result preparation.
• The result batch was prepared locally and was not posted publicly.

Release note

After this PR is merged, a maintainer can decide whether to push v0.3.0; that tag triggers publication of the GHCR image.