fix: trust-only kodo.toml causes spurious warning on build

[rfunix]

Problem

After #59, a kodo.toml containing only a [trust] section (without module/version) caused two issues:

1. load_trust_config used read_manifest which requires the full Manifest struct — parse failed silently but the trust config was not loaded
2. run_build called read_manifest separately for dependency resolution and printed a noisy warning: error: could not parse kodo.toml to stderr

Fix

manifest.rs

Introduced a TrustOnlyManifest struct (only trust: Option<TrustSection>) used exclusively by load_trust_config. A minimal kodo.toml like this now works correctly:

[trust]
known_agents    = ["claude", "gpt-4", "copilot", "gemini"]
human_reviewers = ["alice", "bob"]

commands/build.rs

Changed the dependency-loading path to silently return Vec::new() when read_manifest fails — a trust-only config has no deps, so skipping dep resolution is the correct behaviour with no need for a warning.

Test plan

• cargo check --workspace — clean
• cargo test --workspace — all pass
• A project with only [trust] in kodo.toml now compiles with no warnings and trust enforcement active

🤖 Generated with Claude Code