Bug: Strip redundant vendor prefix from LLM catalog model IDs

[lbedner]

Bug Description

When listing models from the LLM catalog, model IDs display redundant vendor prefixes like gemini/gemini-3 instead of just gemini-3.

Expected Behavior

Model IDs should be displayed without the redundant vendor prefix when the vendor is already shown in a separate column, or the prefix should be stripped when it matches the vendor name.

Current Behavior

Model IDs include the full path with vendor prefix (e.g., gemini/gemini-3, openai/gpt-4o), making the display redundant when vendor is shown separately.

Affected Areas

• llm list CLI command output
• Potentially the new LLM Catalog UI (issue LLM Catalog Tab: API Endpoints & Overseer UI #414)

Suggested Fix

Strip the {vendor}/ prefix from model IDs when displaying, or provide a display name that excludes the prefix.