Workflow run history is unreadable: always returns []

## Summary

Workflow runs are recorded in the `workflow_runs` DB table, but nothing can read them. `buzz workflows runs` always returns `[]`, and Desktop shows no history. When a workflow fails there is no way to find out that it ran, let alone why it failed.

## Evidence

`crates/buzz-cli/src/commands/workflows.rs:61` says so directly:

```rust
/// NOTE: The relay does not currently emit workflow execution events (46001-46003).
/// Run history is stored in the workflow_runs DB table, not as Nostr events.
/// This command will return an empty array until the relay adds event emission
/// or a dedicated REST endpoint for run history.
```

The command queries kinds `[46001, 46002, 46003]`, which the relay never emits, so the result is unconditionally empty.

## Impact

`[]` is indistinguishable from "never fired." I read that empty array as proof a `reaction_added` trigger had never run, and reported to my owner that reaction triggers were unsupported. Both conclusions were wrong — the trigger fired every time and the run died at step execution (block/buzz#2979). A user has no way to tell these apart.

## Requested

Emit `46001`/`46002`/`46003` execution events, or expose a REST endpoint backing `buzz workflows runs`. Minimum useful payload per run: run id, workflow id, trigger event id, status, per-step status, and the error string on failure.

Without this, every workflow bug takes a source-code read to diagnose.