feat: massive overhaul to manage costs (#103)

### Explanation

_No response_

### Issue

Closes #102

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- [ ] 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

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### Versioning

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Reviewed-on: #103
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/lib/tauri.ts

@@ -90,6 +90,11 @@ interface OutputPayload {
   content: string;
   tool_name: string | null;
   conversation_id?: string;
+  cost?: {
+    input_tokens: number;
+    output_tokens: number;
+    cost_usd: number;
+  };
 }
 
 interface ConnectionPayload {
@@ -242,7 +247,16 @@ export async function initializeTauriListeners() {
   unlisteners.push(stateUnlisten);
 
   const outputUnlisten = await listen<OutputPayload>("claude:output", (event) => {
-    const { line_type, content, tool_name, conversation_id } = event.payload;
+    const { line_type, content, tool_name, conversation_id, cost } = event.payload;
+
+    // Convert snake_case cost to camelCase for TypeScript
+    const costData = cost
+      ? {
+          inputTokens: cost.input_tokens,
+          outputTokens: cost.output_tokens,
+          costUsd: cost.cost_usd,
+        }
+      : undefined;
 
     // Always store the output to the correct conversation
     if (conversation_id) {
@@ -250,14 +264,16 @@ export async function initializeTauriListeners() {
         conversation_id,
         line_type as "user" | "assistant" | "system" | "tool" | "error",
         content,
-        tool_name || undefined
+        tool_name || undefined,
+        costData
       );
     } else {
       // Fallback to active conversation if no conversation_id provided
       claudeStore.addLine(
         line_type as "user" | "assistant" | "system" | "tool" | "error",
         content,
-        tool_name || undefined
+        tool_name || undefined,
+        costData
       );
     }
   });