Fix Cursor provider for newer versions

[iamtoruk]

Summary

Newer Cursor versions store conversation data in agentKv:blob:* entries instead of populating tokenCount in bubbleId entries. This caused the Cursor provider to return zero usage.

Changes

• Add fallback parser that reads agentKv entries when bubbleId returns no results
• Estimate tokens from content length (~4 chars per token)
• Extract model info from providerOptions.cursor.modelName

Test Results

Before: cost: 0, calls: 0
After: cost: 0.04, calls: 4, input: 1474, output: 4197

Closes #114
Closes #102