Add totalTokens field to Usage type

- Added totalTokens field to Usage interface in pi-ai
- Anthropic: computed as input + output + cacheRead + cacheWrite
- OpenAI/Google: uses native total_tokens/totalTokenCount
- Fixed openai-completions to compute totalTokens when reasoning tokens present
- Updated calculateContextTokens() to use totalTokens field
- Added comprehensive test covering 13 providers

fixes #130

packages/web-ui/example/src/main.ts

@@ -131,6 +131,7 @@ const saveSession = async () => {
 				output: 0,
 				cacheRead: 0,
 				cacheWrite: 0,
+				totalTokens: 0,
 				cost: {
 					input: 0,
 					output: 0,