Show helpful message when Gemini CLI fails with trust directory error

[benthomasson]

Problem

When Gemini CLI is not trusted for a workspace, code-review reports a cryptic BLOCK verdict with the raw error. This has been happening on every review recently since Gemini CLI added workspace trust as a security requirement.

Current behavior

## gemini [BLOCK]

### ERROR
**Verdict:** BLOCK

Model invocation failed: Model gemini failed: Gemini CLI is not running in a trusted directory...

Proposed behavior

Detect the trust directory error and show a helpful message:

## gemini [SKIPPED]

Gemini CLI requires workspace trust. To fix, run interactively in this repo:

    cd /path/to/repo && gemini
    # then type /trust

See: https://geminicli.com/docs/cli/trusted-folders/

Notes

• Should not suggest GEMINI_CLI_TRUST_WORKSPACE=true as the fix — that blanket-trusts all workspaces
• Per-directory trust via /trust in interactive mode is the safe approach
• The review should continue with remaining models rather than reporting BLOCK