Wire governance CLI subcommands into main.rs

[jeremymanning]

Parent: #7

Wire governance CLI (propose, list, vote, report) from src/cli/governance.rs into main.rs. Subcommand struct exists.

Files: src/main.rs, src/cli/governance.rs

[jeremymanning]

Resolved by PR #58 (spec 003-stub-replacement). All 77 tasks complete, 489+ tests passing, CI green on Linux/macOS/Windows.