refactor(remote-git): remove obsolete HTTP browser example

[forhappy]

Summary

Remove the standalone browse_http Axum demo now that the repository HTTP server provides the complete browsing UI.

• Delete the bundled browser example and its HTML asset.
• Remove the Axum, RNG, and Serde-only example dependencies and unused Tokio features.
• Keep qualify_browse and verify_remote_browse.py for remote-only correctness qualification.
• Keep the remote Git library, tests, and production repository UI unchanged.

Validation

• CARGO_TARGET_DIR="$HOME/Workspace/crabbuild-target/crab-pr149" cargo check -p crab-remote-git --all-targets
• CARGO_TARGET_DIR="$HOME/Workspace/crabbuild-target/crab-pr149" cargo test -p crab-remote-git --all-targets (106 unit tests, 72 integration tests passed)
• cargo fmt --all -- --check
• git diff --check