Docs: add small glossary entry for avoided model-call events

[hkalbertkim]

Goal

Add a concise glossary entry explaining avoided model-call events.

Suggested files

• docs/glossary.md or docs/telemetry-and-observability.md

Acceptance criteria

• Defines the term in local/no-network validation context and does not convert it into production cost savings.
• Keeps the change small and suitable for a first contribution.
• Does not introduce secrets, private data, raw provider responses, or unsupported claims.

Validation

git diff --check

[iitcsdev]

Hi! I'd like to work on this issue and submit a PR for it.

[hkalbertkim]

Sure