fix(bugs): print empty-results hint when --vulns alone yields no matches (#264)

## Summary
Follow-up to #254. That PR introduced `empty_filter_hint` with a
dedicated *"No security vulnerabilities found with the current
filters."* branch — and a unit test
(`empty_filter_hint_vulns_flag_with_empty_prefilter`) asserting that
exact message — but only wired the helper into the `--introduced-by`
branch of the handler. When a user runs `detail bugs list --vulns`
without an author filter and zero vulnerabilities match, the helper is
never reached: they just see an empty table with no explanation.

Add the matching early return for the `--vulns`-alone case: if the
post-`--vulns` filter is empty and `--introduced-by` wasn't given, print
the hint and return.

## Test plan
- [x] `cargo test --lib bugs::` — 35 pass
- [x] `cargo clippy -- -D warnings` clean
- [x] `cargo fmt --check` clean
- [ ] Manual: `detail bugs list <repo-without-vulns> --vulns` now prints
"No security vulnerabilities found with the current filters." instead of
an empty table

Fixes #259.

🤖 Generated with [Claude Code](https://claude.com/claude-code)
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Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: sachiniyer

src/commands/bugs.rs

@@ -337,6 +337,16 @@ pub async fn handle(command: &BugCommands, cli: &crate::Cli) -> Result<()> {
                         }
                         return output_list(&filtered, 0, *page, *limit, format);
                     }
+                } else if filtered.is_empty() {
+                    // `--vulns` alone filtered everything out. Without this
+                    // branch the user just sees an empty table and no hint,
+                    // even though `empty_filter_hint` already has the right
+                    // message for this case.
+                    if matches!(format, crate::OutputFormat::Table) {
+                        let hint = empty_filter_hint(&filtered, *vulns);
+                        Term::stdout().write_line(&hint)?;
+                    }
+                    return output_list(&filtered, 0, *page, *limit, format);
                 }
                 let total = filtered.len();
                 let page_items = paginate_items(&filtered, *page, *limit);