fix: show proper conflict error between --output and --remote-name

[ryanfowler]

Summary

conflicts_with (singular) on the --output flag caused clap to emit a misleading error message when -o and -O were used together:

$ fetch -o /tmp/a -O https://example.com
error: flag '--output' cannot be used multiple times

Fix

Changed conflicts_with = "remote_name" to conflicts_with_all = ["remote_name"] on the output argument at src/cli.rs:399, matching the convention used by remote_name and discard. This makes the conflict definition symmetric, so clap now reports:

$ fetch -o /tmp/a -O https://example.com
error: flags '--output' and '--remote-name' cannot be used together

Validation

• cargo build --locked
• cargo test --locked --all-features --test cli — 14/14 passed
• Manual smoke test with -o + -O produces the correct error message