feat: add opencode agent support (#18)

## Summary
- Add OpenCode to the known agents list with process name `opencode` and
attribution email

## Test plan
- [x] Lookup test added for `opencode`

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

Co-authored-by: Bradley Dwyer <bradleydwyer@block.xyz>

Author: bradleydwyer

src/agent.rs

@@ -97,6 +97,13 @@ pub const KNOWN_AGENTS: &[Agent] = &[
         email: "opencode <noreply@opencode.ai>",
         ..Agent::default()
     },
+    Agent {
+        process_names: &["opencode"],
+        env_vars: &[],
+        email: "OpenCode <noreply@opencode.ai>",
+        breadcrumb_dir: None,
+        breadcrumb_ext: None,
+    },
 ];
 
 impl Agent {

src/main.rs

@@ -316,6 +316,7 @@ mod tests {
         assert!(Agent::find_by_name("/opt/homebrew/bin/amp").is_some());
         assert!(Agent::find_by_name("gemini").is_some());
         assert!(Agent::find_by_name("goose").is_some());
+        assert!(Agent::find_by_name("opencode").is_some());
         assert!(Agent::find_by_name("unknown").is_none());
     }