feat: add private AI tracing with AgentPond

[marcusschiesser]

Summary

• initialize the AgentPond Firebase exporter through Firebase Functions onInit() after the default Admin app exists
• register OpenInference's OpenAI instrumentation before the OpenRouter-backed client loads
• redact forwarded-email prompts and generated calendar content while retaining model, token, latency, and error metadata
• keep the AgentPond skills installed by npx agentpond@0.5.2 init

Why AgentPond

AgentPond makes fwd2cal's AI event extraction observable without adding a separate hosted tracing backend. Its OpenInference spans can show which model handled an email, how many tokens it used, how long extraction took, and whether a retry or structured-output failure occurred. That is especially useful for diagnosing emails that do not become valid calendar events. Trace batches stay in project-controlled Firebase Storage and can be synced for local DuckDB analysis.

Prompt and completion bodies are redacted by default because forwarded emails can contain personal or confidential information.

Verification

• npm run lint
• npm run build
• npx tsc -p tsconfig.json --noEmit
• loaded the compiled Functions entrypoint and completed the async AgentPond onInit() path with a synthetic Firebase config
• exercised a real gpt-4o-mini request and observed an OpenInference LLM span with model and token metadata; input.value and output.value were both __REDACTED__

The repository's full test script was not run because it starts emulators, waits for an interactive Google OAuth login, and opens a browser. No deployment was performed.

Firebase Storage status

This repository does not currently configure Cloud Storage or Storage Rules in firebase.json, so this PR does not invent a rule override or claim that production access is verified. Before deployment, the project needs a configured default bucket and maintainer verification that no client rule can read or write agentpond/**. Live Firebase export, agentpond sync, and trace listing could not be verified without production bucket access.