Fix remaining clippy warnings

- Replace segments.last() with segments.next_back() for DoubleEndedIterator
- Replace format!() with .to_string() for static strings
- Fixes all clippy warnings causing CI failures

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: tdi

src/agent.rs

@@ -63,7 +63,7 @@ impl Agent {
             // For non-GitHub URLs, use the last segment as filename
             parsed_url
                 .path_segments()
-                .and_then(|segments| segments.last())
+                .and_then(|mut segments| segments.next_back())
                 .ok_or_else(|| anyhow::anyhow!("Invalid URL"))?
                 .to_string()
         };

src/commands/doctor.rs

@@ -107,9 +107,8 @@ pub fn execute(fix: bool) -> Result<()> {
                 issues.push(Issue {
                     agent_name: name,
                     issue_type: IssueType::UnmanagedFile,
-                    description: format!(
-                        "Regular file in .claude/agents/ should be managed via ccagents"
-                    ),
+                    description: "Regular file in .claude/agents/ should be managed via ccagents"
+                        .to_string(),
                     fixable: true,
                 });
             }