fix: capture accurate usage (#80)

### Explanation

_No response_

### Issue

_No response_

### Attestations

- [ ] I have read and agree to the [Code of Conduct](https://docs.nhcarrigan.com/community/coc/)
- [ ] I have read and agree to the [Community Guidelines](https://docs.nhcarrigan.com/community/guide/).
- [ ] My contribution complies with the [Contributor Covenant](https://docs.nhcarrigan.com/dev/covenant/).

### Dependencies

- [ ] I have pinned the dependencies to a specific patch version.

### Style

- [ ] I have run the linter and resolved any errors.
- [ ] My pull request uses an appropriate title, matching the conventional commit standards.
- [ ] My scope of feat/fix/chore/etc. correctly matches the nature of changes in my pull request.

### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
- [ ] All new and existing tests pass locally with my changes.
- [ ] Code coverage remains at or above the configured threshold.

### Documentation

_No response_

### Versioning

_No response_

Reviewed-on: #80
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src-tauri/src/wsl_bridge.rs

@@ -704,7 +704,7 @@ fn process_json_line(
             subtype,
             result,
             permission_denials,
-            usage: _,
+            usage,
             ..
         } => {
             let state = if subtype == "success" {
@@ -713,6 +713,21 @@ fn process_json_line(
                 CharacterState::Error
             };
 
+            // Track token usage from Result messages if available
+            // This captures tokens from tool outputs and other operations
+            if let Some(usage_info) = usage {
+                // We need the model info to calculate cost properly
+                // For now, use the last known model from stats
+                let model = {
+                    let stats_guard = stats.read();
+                    stats_guard.model.clone().unwrap_or_else(|| "claude-opus-4-20250514".to_string())
+                };
+
+                let mut stats_guard = stats.write();
+                stats_guard.add_usage(usage_info.input_tokens, usage_info.output_tokens, &model);
+                println!("Result message tokens - input: {}, output: {}", usage_info.input_tokens, usage_info.output_tokens);
+            }
+
             // Always emit updated stats on result message (less frequent)
             // This includes the latest session duration
             let newly_unlocked = {