feat(acp): add OpenCode and Cursor runtimes

[austin-thesing]

Summary

• discover OpenCode and Cursor Agent as native ACP runtimes in Buzz Desktop
• normalize their launch arguments to acp, including Cursor’s agent and cursor-agent commands
• document standalone buzz-acp configuration for both runtimes

Verification

• opencode acp --help
• agent acp --help
• cursor-agent acp --help
• cargo test -p buzz-acp normalizes_acp_subcommand_runtimes_to_acp
• cargo test --manifest-path desktop/src-tauri/Cargo.toml --lib managed_agents::discovery::tests::normalizes_opencode_and_cursor_args_to_acp
• cargo test --manifest-path desktop/src-tauri/Cargo.toml --lib managed_agents::discovery::tests::opencode_and_cursor_are_known_native_acp_runtimes
• cargo fmt --all -- --check
• git diff --check

Note

The broader cargo test -p buzz-acp config::tests suite has one unrelated macOS fixture failure in test_load_rules_empty_name_rejected: its attempted temporary filename is rejected with Invalid argument.

[austin-thesing]

I realize this is similar to #2370 but would appreciate both Cursor & OpenCode acp additions to Buzz

[chatgpt-codex-connector]

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